Hundreds of Fatah supporters fled the Hamas-controlled Gaza Strip by land and sea on Saturday and the Islamist group threatened to take its fight against Palestinian President Mahmoud Abbas's forces to the West Bank.
Abbas, who leads the secular Fatah faction, plans to swear in an emergency government on Sunday that will bring an end to a US-led aid embargo. Prime Minister-designate Salam Fayyad has selected 14 ministers to serve in his cabinet, officials said.
Hamas official Sami Abu Zuhri said 150 Hamas supporters were "abducted" in the occupied West Bank in what he called acts of "real terrorism" by Fatah forces there. "We will not stand handcuffed against these crimes in the West Bank. We will take all steps to secure an end to these crimes," he said.
The US consul-general who handles relations with the Palestinians said Washington would lift a ban on direct financial aid to the new emergency government, clearing the way for the European Union and Israel to follow suit.
"There won't be any obstacles economically and politically in terms of re-engaging with this government ... They will have full support," Jacob Walles told Reuters after meeting Abbas at his West Bank headquarters in Ramallah, near Jerusalem.
Hamas said it did not seek its own state in Gaza, where 1.5 million people live crowded along 40 km (25 miles) of coast. Western powers imposed an aid embargo after Hamas came to power in March 2006 because it failed to recognise Israel, renounce violence and accept interim peace deals. An Israeli army spokeswoman said Israel had allowed people to leave Gaza for the West Bank on a case-by-case basis.
In Hebron, another West Bank city, militants of al Aqsa Martyrs Brigades, an offshoot of Fatah, stormed government offices and set up checkpoints to search for Hamas members. Many Fatah supporters in Gaza fear reprisals from Hamas. "We were destroyed... I feel lost," said Umm Rami, whose husband is a colonel in the Fatah-dominated National Security Forces. Under Palestinian law, Abbas can declare a state of emergency for up to 30 days.
The state of emergency could be extended for another 30 days, but only after winning the approval of two thirds of parliament. Hamas has a majority in the parliament although Israel's arrests of nearly half of Hamas's deputies put that majority in doubt and also made it hard to achieve a quorum.