Much of the country has been in uproar since the military deposed civilian leader Aung San Suu Kyi on February 1, with large street demonstrations seen in major cities and isolated villages alike.

Authorities have responded with increasing force, deploying troops against peaceful rallies and firing tear gas, water cannon and rubber bullets, with isolated incidents of live rounds being used.

In Mandalay on Saturday, a shipyard raid turned violent when security forces opened fire on protesters trying to stop the arrest of marine staff taking part in the anti-coup movement.

The skirmish started with the demonstrators flinging rocks, but authorities retaliated by opening fire -- sending them fleeing in fear.

In a video livestreamed on Facebook by a resident hiding nearby, continuous gunfire could be heard.

"Two people were killed," said Hlaing Min Oo, the chief of a Mandalay-based volunteer emergency rescue team, adding that one of the victims, who was shot in the head, was a teenager.

The death toll was confirmed by another emergency worker on the scene, who declined to be named for fear of repercussions.

"One under-18 boy got shot in his head," he told AFP.

Graphic video circulated on Facebook of the boy, splayed on the ground and bleeding from his head as a bystander placed a hand on his chest to feel for a heartbeat.

"About 30 others were injured -- half of the injured people were shot with live rounds," Hlaing Min Oo said, adding the rest had rubber bullet and slingshot wounds.

The use of live rounds was also confirmed by doctors and other aides working on the ground, though they declined to be named.

Local media reported more than a dozen people were arrested after the clash.

"They beat and shot my husband and others," a resident told AFP in tears. "He was standing on the side and watching the protest but the soldiers took him away."

Police could not be reached for comment.

The city had previously seen a clash on Monday, which left at least six injured after police and soldiers fired rubber bullets into a crowd of protesters, who threw bricks at them in return.

- 'We cannot accept police crackdowns' -

The clash in Mandalay comes as the country mourns the death of a 20-year-old anti-coup protester who was shot in the head last week in Myanmar's capital Naypyidaw.

On Saturday, thousands gathered at the main junctions of Yangon, Myanmar's largest city -- though the crowds appeared smaller than in recent days.

"I feel that the bullet that hit Mya Thwate Thwate Khaing's head has also hit our heads," said protester Win Zaw, 46.

"We cannot accept the police crackdowns because these are undisciplined, beyond our laws."

Condemnation of the violence has been fierce, and US Secretary of State Antony Blinken has held talks with allied countries in recent days to press for a firm international response.

"We reiterate our calls on the Burmese military to refrain from violence against peaceful protesters," spokesman Ned Price told reporters Friday.

The military regime has so far weathered a chorus of international condemnation, with US, Britain and Canada having all announced sanctions targeting the country's top generals.

The junta has justified its power seizure by alleging widespread electoral fraud in November's elections, which Suu Kyi's party won in a landslide.

- Hundreds arrested -

Nearly 550 people have been arrested, charged or sentenced since the coup, according to the Assistance Association for Political Prisoners (AAPP), with 500 still behind bars.

Among those targeted have been railway workers, civil servants and bank staff who have walked off their jobs as part of a civil disobedience campaign aimed at crippling the army's ability to govern.

There have also been isolated reports of members of the security forces taking part in nationwide protests, including a soldier in remote Sagaing region whose participation went viral.

But by Saturday, the military's information team released a video of the soldier, sergeant clerk Than Lwin, sitting straight-back against a wall, claiming he was drunk when he joined the protesters.

"They used me to ruin my life," Than Lwin said of the protesters, in the confession-style video.

Authorities have maintained that methods used to disperse protesters are according to the law, and a military spokesman said this week that one police officer had died in Mandalay after a clash.

Suu Kyi -- who has not been seen since she was detained in a dawn raid -- has been hit with two charges, one of them for possessing unregistered walkie-talkies.

Her hearing is expected on March 1.