Two people were killed during clashes at a protest in the country's second-biggest city Mandalay, a witness and media reports said, and one person was killed when police opened fire in the main city of Yangon, a witness there said.

The Monywa Gazette reported five people were killed in that central town in police firing. One person was shot and killed in the central town of Myingyan, said student activist Moe Myint Hein, 25.

"They opened fire on us with live bullets. One was killed, he's young, a teenage boy, shot in the head," Myint Hein, who was wounded in the leg, told Reuters by telephone.

The latest violence came a day after foreign ministers from Southeast Asian neighbours urged restraint but failed to unite behind a call for the military to release ousted government leader Aung San Suu Kyi and restore democracy.

At least 30 people have been killed since the coup on February 1, which ended Myanmar's tentative steps towards democratic rule, triggering nationwide protests and international dismay.

The security forces also detained about 300 protesters as they broke up protests in Yangon, the Myanmar Now news agency reported.

Video posted on social media showed long lines of young men, hands on heads, filing into army trucks as police and soldiers stood guard.

The Monywa Gazette reported five people were wounded in that central town when security forces fired live ammunition. There were unconfirmed reports of firing and injuries in another central town, Magway.

On Tuesday, the Association of Southeast Asian Nations (ASEAN) failed to make a breakthrough in a virtual foreign ministers' meeting on Myanmar.

While united in a call for restraint, only four members - Indonesia, Malaysia, the Philippines and Singapore - called for the release of Suu Kyi and other detainees.

"We expressed ASEAN's readiness to assist Myanmar in a positive, peaceful and constructive manner," the ASEAN chair, Brunei, said in a statement.

Myanmar's state media said the military-appointed foreign minister attended the ASEAN meeting that "exchanged views on regional and international issues", but made no mention of the focus on Myanmar's problems.

It said Wunna Maung Lwin "apprised the meeting of voting irregularities" in November's election.

The military justified the coup saying its complaints of voter fraud in the November 8 elections were ignored. Suu Kyi's party won by a landslide, earning a second five-year term. The election commission said the vote was fair.

Junta leader Senior General Min Aung Hlaing has said the intervention was to protect Myanmar's fledgling democracy and has pledged to hold new elections but given no time frame.

Singapore Prime Minister Lee Hsien Loong said on Tuesday in an interview the coup was a "tragic" step back for Myanmar and the use of lethal force by its security forces was "disastrous".

ASEAN's bid to find a way out of the crisis has drawn criticism from inside Myanmar, with concern it would legitimise the junta and not help the country.

"No more words, action," activist Thinzar Shunlei Yi told Reuters in a message when asked about the ASEAN effort. She called for sanctions on businesses linked to the military.

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.

She is one of nearly 1300 people who have been detained, according to activists, among them six journalists in Yangon.

Australian Associated Press