- UN envoy says 38 killed in Wednesday's violence.
- Security forces opened fire with live rounds in several towns.
- Suu Kyi's party says flags to fly at half mast at its offices.
- UN Security Council to discuss situation on Friday – diplomats.
Police in Myanmar broke up demonstrations in several places with tear gas and gunfire on Thursday as protesters took to the streets again undeterred by the rising death toll in a crackdown on opponents of last month's military coup.
The incidents followed the bloodiest day since the military overthrew the elected government of Aung San Suu Kyi on Feb. 1, with the United Nations special envoy on Burma saying 38 people had been killed on Wednesday.
The United Nations human rights chief, Michelle Bachelet, called on the security forces to halt what she called their "vicious crackdown on peaceful protesters".
At least 54 people had been killed in total but the actual toll could be much higher, she said. More than 1,700 people had been arrested, including 29 journalists.
"Myanmar's military must stop murdering and jailing protesters," Bachelet said in a statement.
Activists said they refused to accept military rule and were determined to press for the release of the detained Suu Kyi and recognition of her victory in a November election.
"We know that we can always get shot and killed with live bullets but there is no meaning to staying alive under the junta," activist Maung Saungkha told Reuters.
Police opened fire and used tear gas to break up protests in Yangon and the central town of Monywa, witnesses said. Police also fired in the town of Pathein, west of Yangon, and used tear gas in Taunggyi in the east, media reported.
In Yangon, hundreds of protesters soon assembled again to chant slogans and sing.
Big crowds also gathered peacefully for rallies elsewhere, including the second city of Mandalay and in the historic temple town of Bagan, where hundreds marched carrying pictures of Suu Kyi and a banner saying: "Free our leader", witnesses said.
Hundreds of people attended the funeral of a 19-year-old woman shot dead in Mandalay on Wednesday, who was photographed wearing a T-shirt that read "Everything will be OK". .
On Wednesday, police and soldiers opened fire with live rounds with little warning in several cities and towns, witnesses said.
"Myanmar's security forces now seem intent on breaking the back of the anti-coup movement through wanton violence and sheer brutality," said Richard Weir, a researcher at Human Rights Watch.
A spokesman for the ruling military council did not answer telephone calls seeking comment.
Suu Kyi's National League for Democracy party said in a statement that flags would fly at half mast at its offices to commemorate the dead.
The UN Security Council is due to discuss the situation on Friday in a closed meeting, diplomats said.
US State Department said Washington was "appalled" by the violence and was evaluating how to respond.
The European Union suspended its support for development projects in Myanmar to avoid providing financial assistance to the military, officials said on Thursday.
The support in past years has involved more than 200 million euros ($240.7 million) in separate programmes often running for four years.
Myanmar's generals have long shrugged off outside pressure.
The UN special envoy for Myanmar, Christine Schraner Burgener, said on Wednesday she had warned deputy military chief Soe Win that the army was likely to face strong measures from some countries over the coup.
"The answer was: 'We are used to sanctions, and we survived'," she told reporters in New York. "When I also warned they will go (into) isolation, the answer was: 'We have to learn to walk with only few friends'."
The United States has told China, which has declined to condemn the coup, it expects it to play a constructive role.
The turmoil has alarmed Myanmar's Southeast Asian neighbours but an effort by some to encourage dialogue has come to nothing.
Singapore, the biggest foreign investor in Myanmar in recent years, advised its nationals to consider leaving as soon as they could due to the violence while it was still possible to do so.
At least 19 Myanmar police officers have crossed over into India, fearing persecution for disobeying orders, a senior Indian police official told Reuters.
The military justified the coup by saying its complaints of voter fraud in the Nov. 8 vote were ignored. Suu Kyi's party won by a landslide, earning a second term. The election commission said the vote was fair.
Junta leader Senior General Min Aung Hlaing has pledged to hold new elections but given no time frame.
Suu Kyi, 75, has been held incommunicado since the coup but appeared at a court hearing via video conferencing this week and looked in good health, a lawyer said.