Air strikes by Myanmar's military killed more than 60 people, including singers and musicians, attending an anniversary celebration of the Kachin ethnic minority's main political organisation, members of the group and a rescue worker said Monday.
The reported attack comes three days before Southeast Asian foreign ministers are to hold a special meeting in Indonesia to discuss widening violence in Myanmar.
The number of casualties at Sunday night's celebration by the Kachin Independence Organization in the northern state of Kachin appeared to be the most in a single air attack since the military seized power in February last year from the elected government of Aung San Suu Kyi.
It was impossible to independently confirm details of the incident, though media sympathetic to the Kachin posted videos showing what was said to be the attack's aftermath, with splintered and flattened wooden structures. There was no immediate comment from the military or government media.
Myanmar has been wracked for decades by rebellions by ethnic minorities seeking autonomy, but anti-government resistance increased markedly nationwide with the formation of an armed pro-democracy movement opposing last year's military takeover.