The alleged massacre of at least 35 people in Myanmar has alarmed a top United Nations official, who has called on authorities to examine the event, which opposition activists have blamed on government forces.

The governing military has not responded to the event in Kayah State’s Mo So hamlet on Friday, and junta spokesperson Zaw Min Tun could not be reached for comment.

Soldiers shot on and killed an undefined number of “terrorists with firearms” from groups battling the military administration, according to state media. The state media made no mention of civilian casualties.

U.N. Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator Martin Griffiths said the reports of the killing of the civilians, including at least one child, were credible.

“I condemn this grievous incident and all attacks against civilians throughout the country, which are prohibited under international humanitarian law,” he said in a statement.

Griffiths called for “a thorough and transparent” investigation so the perpetrators could be brought to justice and called for the protection of civilians.

Residents and a human rights group working in the area said soldiers had killed the civilians. Photographs posted by the rights group showed charred bodies, some in the back of a burned-out truck.

Myanmar has been in turmoil since the military on Feb. 1 overthrew the elected government of Nobel Prize laureate Aung San Suu Kyi.

More than 1,300 people have been killed in crackdowns on protests and more than 11,000 have been jailed, according to a tally by the Association for Assistance of Political Prisoners rights group.

The number of people killed by the organization is disputed by the military.

Some military opponents have taken up guns, forming alliances with ethnic minority insurgents who have been fighting for self-determination in various regions of the country for years, notably Kayah State in the east.

Two of Save the Children’s staff were reported missing in the attack while returning to their home towns for the holidays. It ceased operations in Kayah State and sections of adjoining Karen State and the Magway area.