The collision of the two Metro North trains forced Amtrak to shut down service indefinitely between New York and Boston, the national railroad said.

Three people were critically injured and 60 people were transported to area hospitals, police said.

"It's pretty devastating damage to a number of cars," Connecticut Governor Dannel Malloy told a news conference. "These cars came into contact (and the impact) ripped open the siding of one of the cars. There is extensive damage in the front and the wheels."

The accident occurred shortly after 6 p.m. EDT (2200 GMT), authorities said.

Republicans and Democrats said senior IRS officials should have alerted Congress last year when they found out that their examiners were singling out Tea Party groups for intense scrutiny when the groups applied for tax-exempt status.

"That isn't being misled. That's lying," said Republican Dave Camp, the chairman of the House of Representatives Ways and Means Committee.

The acting head of the agency, Steven Miller, apologized for the IRS's actions and said they stemmed from poor management, rather than a partisan desire to punish conservative groups.

"I did not mislead Congress or the American people," said Miller, who was fired by President Barack Obama on Wednesday. "I think what happened here is that foolish mistakes were made by people trying to be more efficient."

Obama, a Democrat, is racing to get in front of a scandal that threatens to eclipse his second-term agenda. He has twice appeared in public to condemn the IRS's actions and has promised to cooperate with three congressional investigations and a Justice Department probe. He has, however, resisted demands for a special prosecutor to look into the allegations.

Republicans have angrily accused Obama's administration of using government powers to target political foes. They say the IRS scandal is one example of a federal government that has grown too large and intrusive.

"Is this still America?" asked Republican Representative Kevin Brady of Texas.

AN EXPLOSION OF ADVOCACY GROUPS

An internal IRS watchdog reported this week that IRS investigators had singled out groups that had conservative-sounding phrases such as "Patriot" and "Tea Party" in their titles when they applied for a tax-exempt status.

Such status allows groups to keep their donor lists secret while engaging in limited political activity. Political campaigns, by contrast, must make their donors lists public.

Tea Party groups say they were asked for information such as what books they read. The questioning in some cases took nearly three years, preventing certain groups from participating in the 2010 and 2012 elections.

The IRS watchdog blamed the scandal on ineffective management and bureaucratic confusion.

The IRS has seen the number of groups applying for so-called 501(c)4 status double in the wake of a January 2010 Supreme Court decision that loosened campaign finance rules at a time when it has struggled to monitor existing tax exempt groups.

The top Democrat on the committee, Representative Sander Levin, warned Republicans not to turn the investigation into a partisan witch hunt.

However, he noted that Lois Lerner, the IRS official who made the scandal public last week, did not bring it up when she testified in front of the committee a few days earlier.

"That is wholly unacceptable and one of the reasons we believe Miss Lerner should be relieved of her duty," Levin said.

Two other committees, the House Oversight and Government Reform Committee and the Senate Finance Committee, also will hold IRS hearings next week.

Fazliddin Kurbanov, 30, was detained in Boise as part of a federal counterterrorism operation, before being hit with charges regarding offences in Idaho and neighbouring Utah.

He was charged with conspiracy to provide material support to a foreign terrorist organization, as well providing support to the same group, and possession of a destructive device.

If convicted, Kurbanov could face 15 years in prison for the conspiracy charge and 10 years for possession of a destructive device.

Meanwhile, charges filed in Utah accused Kurbanov of teaching and demonstrating how to make an explosive device via Internet videos. He could face 20 years in prison if convicted on those charges.

"When you attack one human, you attack all human," Tsarnaev also scribbled on the inside wall of the boat where he hid from police during a massive manhunt in the days after the April 15 blasts, according to CBS News.

The twin explosions near the finish line of the Boston Marathon killed three people and wounded more than 260.

Citing unnamed sources, CBS News said the note claimed the bombings were payback for US military action in Afghanistan and Iraq and referred to the victims as "collateral damage."

Dzhokhar also said he did not mourn the death of his older brother Tamerlan, saying he was a martyr after being killed in a shootout with police.

Federal prosecutors have charged Dzhokhar with using and conspiring to use a weapon of mass destruction, as well as the malicious destruction of property by means of deadly explosives.

He faces the death penalty if found guilty.

FBI agents, meanwhile, have searched the home of a former Chechen rebel fighter living in the United States who admits he met with Tamerland Tsarnaev less than a month before the bombings, Voice of America reported.

Musa Khadjimuradov, 35, told VOA that agents took his computer hard drives during a search of his home in Manchester, New Hampshire, along with DNA samples and fingerprints.

Khadjimuradov, who was granted asylum in the United States in 2004, said the FBI told him he was not a suspect in the case.

He denied any involvement but told VOA: "I believe they (were) thinking like he (was) up in New Hampshire (and) like I tried to help him or do something, you know, like that."

The case also allegedly involves three young students, two from Kazakhstan and an Ethiopian-American.

The Kazakhs -- Dias Kadyrbayev and Azamat Tazhayakov -- are being held on charges of covering up for the Tsarnaev brothers.

According to prosecutors, the two went to Dzhokhar's dorm room at the University of Massachusetts, where they were all studying, and took his backpack and laptop and threw them away.

The third friend of the younger Tsarnaev, Robel Phillipos, was accused of lying to investigators after the blasts. He was ordered free on $100,000 bail May 6 as he awaits trial.

A lawyer for Tazhayakov said his client denies the charges against him.

"As far as where the case is going, the government alleges that my client gave consent for another defendant, Kadyrbayev, to enter the dorm room, which somehow created a conspiracy," Arkady Bukh told AFP.

"We are trying to get more evidence in order to intelligently assess the case. At this time, my client is denying any involvement in the crime."

A hearing scheduled for the two Kazakhs was canceled on Tuesday to give the parties more time to prepare.

Sunday's shooting at a crowded parade filled with families shocked the Big Easy, which is struggling to overcome what mayor Mitch Landrieu described as "the relentless drumbeat of violence" on its streets.

Most of the victims escaped with non-life threatening injuries after they were grazed by the bullets sprayed into the crowd, but two 10-year-old children were among those shot.

Akein Scott, 19, was booked into custody at about 3 am Thursday on 20 counts of attempted murder.

The New Orleans police could not confirm reports that he is a gang member.

"This is an ongoing investigation. We don't know what his affiliation is," spokesman Frank Robertson told AFP.

Police believe that at least two guns were used in the shooting and officers who were marching with the parade saw three suspects running away after the shooting. However, Scott's photo was the only one released to the media.

Scott was out of jail on a $15,000 bond at the time of the shooting after pleading not guilty to charges of illegally carrying a weapon last month. He had also been charged with resisting arrest and heroin possession, according to the Orleans parish sheriff's department.

He had previously been arrested last year for possession of a stolen weapon, but the charges appear to have been dropped.

At least three twisters were confirmed to have struck on Wednesday night, the deadliest tornadoes to hit the United States so far this year, destroying homes and uprooting trees.

The worst damage was reported in Granbury, a town of 8,000 people about 35 miles (56 km) southwest of Dallas-Fort Worth.

Granbury Mayor Pro Tem Nin Hulett told ABC News on Thursday that the top priority "is to try to get the people that are out there in the community under a shelter somewhere" and to account for the missing.

Hood County Sheriff Roger Deeds said 14 people remained unaccounted for, as rescue workers searched houses.

"I've had information that people were found in homes, they were hard hit, those homes. I've been told (they) were collapsed, destroyed as they were probably hit by flying debris," Deeds told CNN.

Hulett said authorities did expect to find people trapped in their homes.

All six of the people confirmed killed were found in Rancho Brazos, a neighborhood of around 110 mostly single family homes on the fringe of Granbury that bore the brunt of the winds, Deeds said.

"Power lines were down, homes were heavily damaged to destroyed and the roads were blocked with debris," Deeds said.

Bulldozers were clearing roads so people could be moved out of their houses.

Matt Zavadsky, a spokesman for MedStar Mobile Healthcare, an agency that provides ambulance service to the region, said about 100 people were injured in the Granbury twister.

There was no immediate estimate for the extent of property damage, but Sheriff's Lieutenant Kathy Jividen said a number of homes were destroyed and trees downed.

TORNADO SEASON

The tornado season in the United States typically starts in the Gulf Coast states in the late winter, and then moves north with the warming weather, peaking around May and trailing off by July.

Several deadly tornadoes have struck in recent years.

In March 2012, at least 39 people were killed in a chain of tornadoes from the Midwest to the Gulf of Mexico. The following month, at least six people were killed by a twister in an Oklahoma town during a weekend outbreak of dozens of twisters across the Great Plains.

In May 2011, a massive tornado struck Joplin, Missouri, killing 161 people and damaging or destroying 7,500 homes.

On Thursday, the Hood County Sheriff Deeds said a "very big percentage" of the homes in Rancho Brazos were devastated. About 90 people were cleared from the area on buses to a school and then to relocation centers.

In Granbury, Pastor Dean Porter of Lake Granbury Christian Temple told Dallas/Fort Worth ABC affiliate WFAA that looking out the front porch of his church at the parking lot he began to see "what looked to be a circular formation" and he ran back inside.

"This particular night is not like anything that I've ever seen," Porter told the station.

Properties were damaged but no one was injured in nearby Parker County, bordering Hood County, Parker County Judge Mark Riley said.

The fatalities Wednesday night came in the town of Granbury in Hood County as the storm destroyed nearly 120 homes in one neighborhood, CNN reported, quoting county sheriff Roger Deeds.

NBC news quoted him as saying 14 people were unaccounted for.

Medical relief spokesman Matt Zavadsky said about 100 people were injured as an apparent tornado touched down several times in Hood and three other counties.

Officials in Hood could not immediately be reached for comment. The county is southwest of Dallas.

The Dallas Morning News ran photos of swirling dark blue masses in the sky, homes damaged by fallen trees and an 18-wheel truck tipped over onto a compact car.

The future direction of the next Iranian leadership in ongoing talks with world powers about the Islamic republic's suspect nuclear program was also difficult to determine, top State Department officials told US lawmakers.

"There are probably some candidates who would be perceived by us as more interested in looking at the nuclear negotiations in a more positive vein," under secretary of state Wendy Sherman said.

"However the nuclear file is held by the supreme leader and no one else, and he is the final decision maker regarding the nuclear file."

The race for Iran's highest elected office took a stunning turn at the weekend when former president Akbar Hashemi Rafsanjani and top nuclear negotiator Saeed Jalili officially registered for the June 14 election.

President Mahmoud Ahmadinejad is constitutionally barred from seeking a third consecutive term. But on Saturday he endorsed his controversial aide and ex-chief of staff Esfandiar Rahim Mashaei.

Jalili, a known hardliner, is close to Iranian supreme leader Ayatollah Ali Khamenei, and was Wednesday in Istanbul for a new round of talks with EU foreign policy chief Catherine Ashton.

But the final line-up of presidential candidates will not be known until later this month when Iran's Guardians Council releases the approved list of names after the vetting process.

Denouncing "a deliberate and unrelenting level of repression in the lead-up to these elections," Sherman told the Senate Foreign Relations committee that the council was "using vague criteria to eliminate potential candidates."

"Without a transparent process, it is difficult for us to say whether Iran's elections will be free, fair, or represent the will of the Iranian people."

Conservatives were "pushing very hard against Mashaei and Rafsanjani, because they don't see either of those candidates as tough enough," she said.

"We don't know the impact as you may recall in 2009, everyone thought Ahmadinejad was going to be one kind of leader and he's turned out to be quite another kind of leader."

Ahmadinejad's disputed re-election in 2009 sparked massive street protests, leading to a heavy-handed regime crackdown and the arrest of hundreds of journalists, activists and reformist supporters.

"We take no sides in Iran's presidential election," Sherman insisted.

"The decision about who leads Iran is for the Iranian people, who should have every opportunity to express freely and openly their opinions, ideas, and hopes for the future of their country."

The action "calls into question the very integrity of Department of Justice policies toward the press and its ability to balance, on its own, its police powers against the First Amendment rights of the news media and the public's interest," said a letter released Tuesday by the coalition.

The protests came after the US government claimed it was trying to protect American lives when it took the drastic step of seizing journalists' phone records in a probe of what it calls a major security breach.

The letter, sent by the Reporters Committee for Freedom of the Press, said that in the 30 years since the Justice Department issued guidelines governing its subpoena practice for journalist phone records, "none of us can remember an instance where such an overreaching dragnet for newsgathering materials was deployed."

Attorney General Eric Holder defended the action Tuesday, saying it was part of a probe into a security breach which had put the American people at risk.

"I've been a prosecutor since 1976. And I have to say that this is among, if not the most serious a very, very serious leak," Holder said.

"That's not hyperbole. Puts the American people at risk. And trying to determine who is responsible for that, I think, required very aggressive action," he declared.

The investigators' action is believed to be linked to a probe into a story on a foiled terror plot, which they suspect contained leaked information.

The AP said its story disclosed details of a CIA operation in Yemen that stopped an Al-Qaeda plot in 2012 to detonate a bomb on an airplane bound for the United States.

Holder said he had recused himself from the probe because he was interviewed by the FBI about unauthorized disclosures in the matter.

The protest letter was signed by news organizations including Dow Jones, EW Scripps, Gannett, The New York Times, The Newspaper Guild, Time Inc. and the Washington Post.

Criticism grew Wednesday with editorials and other comments from news organizations.

The Washington Post said in an editorial that "whatever national-security enhancement this was intended to achieve seems likely to be outweighed by the damage to press freedom and governmental transparency."

New York Times public editor Margaret Sullivan said in a column, "This was supposed to be the administration of unprecedented transparency instead it's turning out to be the administration of unprecedented secrecy and of unprecedented attacks on a free press."

National Press Club president Angela Greiling Keane said the incident "appears to be a gross violation of press freedom. If there's a good explanation for this, the public has a right to hear it."

Al Tompkins of the Poynter Institute, a media education group, said that the government's ability to seize the logs despite free press protections "reminds me of the fact that North Korea's government has a statute on the books promising free press the Justice Department's guidelines, like North Korea's free-press law, proved worthless as soon as they proved untidy."

One of them was classified as an X3.2 flare, with X-class flares being the most intense type, the US space agency said.

"This is the strongest X-class flare of 2013 so far, surpassing in strength the two X-class flares that occurred earlier in the 24-hour period," NASA said of the latest flare that peaked at 0111 GMT Tuesday.

The flares have sent off bursts of radiation from the Sun, known as coronal mass ejections (CMEs). The most recent traveled particularly fast, at a speed of approximately 1,400 miles (2,253 kilometers) per second, NASA said.

NASA said the CMEs would produce a merged cloud of solar material that "may give a glancing blow to the STEREO-B and Epoxi spacecraft," which are space-based observatories orbiting Earth to monitor solar storms and comets.

"Their mission operators have been notified. If warranted, operators can put spacecraft into safe mode to protect the instruments from solar material," the US space agency said.

Experts say that a rise in solar activity is common right now because the Sun is in a phase of its 11-year activity cycle that is nearing the solar maximum, expected in 2013.

According to space weather experts at the National Oceanic and Atmospheric Administration, more strong solar flares may be expected in the coming days.

Although CMEs send off potent radiation, Earth is protected by its magnetic field.

Solar activity can temporarily disrupt GPS signals and communications satellites, but most people will not notice any effects in their daily lives.

The first X-class flare of this solar cycle occurred in February, 2011. The largest so far of the current cycle was documented as an X6.9 in August 2011.