Myanmar’s ruling junta has confirmed carrying out air strikes on a village in the Sagaing region on Tuesday.
At least 50 people were killed in Pazigyi, including women and schoolchildren, and dozens were wounded.
Zaw Min Tun, a spokesman for the military, said that security forces attacked an opening ceremony of a local office allegedly connected to an opposing militia group and admitted some targets were in "civilian clothes".
The junta said it had "launched limited air strikes" after receiving a tip-off from locals about the event.
Mr Tun blamed some of the deaths on mines planted by the militias — known as the People’s Defence Forces.
There was no official confirmation of the number of deaths, but the military insisted they had tried to minimise civilian casualties.
"We heard that more people were killed because of big explosions from weapons and ammunitions … displayed at the opening event," a junta statement said.
UN Secretary General Antonio Guterres condemned the attack and called for the military to “end the campaign of violence against the Myanmar population throughout the country", demanding “those responsible to be held accountable”.
UN rights chief Volker Turk said he was "horrified" by the deadly air strikes.
Washington also denounced the "reprehensible" attack.
"We strongly condemn the regime's air strikes and urge the regime to cease the violence," US State Department counsellor Derek Chollet tweeted.
The final death toll is estimated to be as high as 100.
The attack is reported to be one of the deadliest since the junta seized power in a military coup more than two years ago.
The attack came as Myanmar was preparing to mark the Buddhist new year — Thingyan — which begins on Thursday.
"As the people of Myanmar celebrate their New Year, the EU is deeply shocked by reports of the latest atrocity committed by the military regime in Sagaing, taking the lives of dozens of innocent civilians," EU foreign affairs representative Nabila Massrali said.
The military last month extended a six-month state of emergency and postponed elections it had promised to hold by August.
The crackdown on dissent following the February 2021 coup that toppled Aung San Suu Kyi's civilian government has left more than 3,200 people dead, according to a local monitoring group.
Sagaing region - near the country's second-largest city of Mandalay - has put up some of the fiercest resistance to the military's rule, with intense fighting raging there for months.
