Rockets and heavy machine guns fired from Afghan government helicopters killed and wounded at least 107 boys and men attending a religious ceremony near the northern city of Kunduz last month, according to a United Nations report on Monday.

Last month, villagers in Dasht-i Archi district of Kunduz said dozens of people, including many children, had been killed in an attack on a religious ceremony, prompting the U.N. to launch an investigation.

The U.N. report underlined the risks of a new strategy, developed with U.S. advisers, which has seen a big buildup in Afghan air power, with rocket-equipped helicopters and attack aircraft deployed to try to break a stalemate with the Taliban.

"A key finding of this report is that the government used rockets and heavy machinegun fire on a religious gathering, resulting in high numbers of child casualties," the United Nations Assistance Mission in Afghanistan (UNAMA) said.

It said at least 36 people, including 30 children, were killed and 71 wounded and there were questions "as to the government's respect of the rules of precaution and proportionality under international humanitarian law."

Investigators verified 107 victims but had received victims' lists from various sources indicating over 200 casualties, the report said.

It said there were serious concerns about the incident that required further investigation but said it was not in a position to determine whether the attack amounted to a violation of international law.