The killings took place on Christmas Eve in eastern Kayah state, where pro-democracy rebels have been fighting the military, which took over the government from the democratically elected administration in February.

In a statement released Wednesday evening, Security Council members "stressed the need to ensure accountability for this act."

They also called "for the immediate cessation of all violence and emphasized the importance of respect for human rights and of ensuring safety of civilians."

The statement said "at least 35 people," including four children and two staff of Save the Children charity, were killed in the attack.

The Security Council also "stressed the need for safe and unimpeded humanitarian access to all people in need, and for the full protection, safety and security of humanitarian and medical personnel."

Anti-junta fighters say they have found more than 30 burnt bodies, including women and children, on a highway in Kayah state following the attack.

Two Save the Children employees have been missing and the rights group confirmed Tuesday that they were among the dead.

Myanmar has been in chaos since the February coup, with more than 1,300 people killed in a crackdown by security forces, according to a local monitoring group.

Self-proclaimed "People's Defense Forces" have sprung up across the country to fight the junta, and drawn the military into a bloody stalemate of clashes and reprisals.

In the aftermath of the attack, Washington renewed calls for an arms embargo on the junta.

Western nations have long restricted weapons to Myanmar's military, which even during the pre-coup democratic transition faced allegations of crimes against humanity for a bloody campaign against the Rohingya minority.

The UN General Assembly voted in June to prevent arms shipments into Myanmar, but the measure was symbolic as it was not taken up by the more powerful Security Council.

China and Russia, which hold veto power on the Security Council -- as well as neighboring India -- are the major arms providers to Myanmar.