BANGKOK -- Myanmar government troops rounded up villagers, some believed to be children, tied them up and slaughtered them, according to a witness and other reports. An opposition leader said the civilians were burned alive, as repression of resistance to a de facto coup takes an increasingly brutal turn.

A video of the aftermath of Tuesday's assault - apparently retaliation for an attack on a military convoy - showed the charred bodies of 11 people, lying in a circle amid what appeared to be the remains of a hut.

Outrage spread both inside and outside Myanmar as graphic images were shared on social media of the assault, which Human Rights Watch said was similar to other recent attacks - and looked like it was meant to be discovered.

“This incident is quite brazen, and it happened in an area that was meant to be found, and seen, to scare people,†researcher for the group, Manny Maung, said. “Our contacts are saying these were just boys and young people who were villagers who were caught in the wrong place at the wrong time.â€

Opposition spokesperson, Dr. Sasa, said the attack began after a military convoy - which was raiding villages in the country's northwest - hit a roadside bomb. Troops retaliated first by shelling the village of Done Taw, then rounding up anyone they could capture there.

“They were lashed together, tortured, and ultimately burned alive,†he said, adding that the victims ranged in age from 14 to 40.

“The sheer brutality, savagery, and cruelty of these acts shows a new depth of depravity, and proves that, despite the pretense of the relative detente seen over the last few months, the junta never had any intention of deescalating their campaign of violence,†said Sasa, who uses one name and is the spokesperson for Myanmar's underground National Unity Government.

That group declared itself the country's only legitimate leaders in the wake of the military takeover on Feb. 1 that prevented elected lawmakers from taking their seats in parliament. The seizure of power was initially met with nonviolent street protests, but after police and soldiers responded with lethal force, violence escalated as opponents of military rule took up arms. In recent months, fighting has been raging in northwestern areas.

UN spokesman Stephane Dujarric expressed deep concern at the reports of the “horrific killing of 11 people†and strongly condemned such violence, saying “credible reports indicate that five children were among those people killed.â€

The government has denied that it had any troops in the area. But a witness told The Associated Press that about 50 troops marched into Done Taw at about 11 a.m. Tuesday, seizing anyone who did not manage to flee.

“They arrested 11 innocent villagers,†said the witness, who described himself as a farmer and an activist and spoke on condition of anonymity because he fears for his safety.

He did not see the moment of their killing but said he believed they were burned alive, as did other people who spoke to Myanmar media.

He later saw the charred remains - and was present when the widely distributed images were taken. The images themselves could not be independently verified.

The witness said that those captured were not members of the locally organized People's Defense Force, which sometimes engages the army in combat. He said they were as members of a less formally organized village protection group and did not give a reason for the soldiers' assault.

Other witnesses cited in Myanmar media said the victims were members of a defense force.

Dujarric, of the UN, reminded Myanmar's military authorities of their obligations under international law to ensure the safety and protection of civilians and called for those responsible “for this heinous act†to be held accountable.

As of Wednesday, he said security forces have killed more than 1,300 unarmed people, including more than 75 children, since the military takeover.

In seizing power, the military claimed there was massive fraud in the 2020 election that saw Aung San Suu Kyi's National League for Democracy win in a landslide. The military said that justified the takeover under a constitution that allows it to seize power in emergencies - though independent election observers did not detect any major irregularities in the voting.

On Monday, Suu Kyi was convicted on charges of incitement and violating coronavirus restrictions and sentenced to two years in prison. The court's action was widely criticized as a further effort by military rulers to roll back the democratic gains of recent years.

Correction:

This story has been updated to correct Manny Maung's title to researcher, not spokesperson.