UN investigators say Myanmar’s military council leaders who ordered the bombing of a school this month that killed 12 children may be responsible for war crimes.

Investigators said that “many reports indicate that the school was shelled for several hours, first with rockets and machine guns from a helicopter, followed by an infantry attack.”

The UN Independent Investigative Mechanism for Myanmar, set up by the UN Human Rights Council in September 2018 to gather evidence of the most serious international crimes, said in a statement that it was “working to criminalize” the attack.

Earlier this month, eyewitnesses told the Associated Press that “two helicopters fired machine guns and heavier weapons at a school in Letit Koni.”

In turn, the government set up by the Myanmar army denied reports that the school had been bombed, accusing the media of distorting the truth.