The Sagaing area in northwest Myanmar was targeted in what is feared to have been the deadliest in a recent wave of strikes by the military. Opponents of the regime described the attack as "senseless and brutal".

UN Human Rights chief Volker Turk condemned the attack, saying it "appears schoolchildren performing dances, as well as other civilians... were among the victims".

Military officials said if innocent civilians had been killed, then it was because they were being "forced to support terrorists".

Kyaw Zaw, a spokesman for the National Unity Government (NUG), an opposing shadow administration, said it believed nearly 100 people were killed when jets dropped bombs on villagers ahead of an attack by helicopter gunships as part of "another senseless, barbaric, brutal attack by the military".

The junta seized power in 2021, ending a decade of reforms which included a civilian government led by Nobel Peace Prize laureate Aung San Suu Kyi.

Some opponents of military rule have taken up arms, while the military has responded with airstrikes and the use of heavy weapons.

UN Secretary-General Antonio Guterres condemned Tuesday's strikes and repeated his call for the military to "end the campaign of violence against the Myanmar population throughout the country".

Junta spokesman Zaw Min Tun told military broadcast channel Myawaddy the attack was carried out on a ceremony held by the NUG.

The event was said to have been in support of the NUG's armed wing, the People's Defence Force (PDF).

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"During that opening ceremony, we conducted the attack. PDF members were killed," said Zaw Min Tun.

"They are the ones opposing the government of the country, the people of the country.

"According to our ground information we hit the place of their weapons' storage and that exploded and people died due to that."

Referring to accusations of civilian casualties, he said "some people who were forced to support them probably died as well".

Residents and media reports put the death toll at between 80 and 100 people, while a PDF member said about 100 bodies, including 16 children, had been cremated following the attack.