Myanmar's military has defended air strikes on a concert organised by an ethnic minority force as a justified response to attacks in the area, after opponents accused the junta of targeting civilians and conducting war crimes.
The air strikes late on Sunday in Kachin State in the north killed at least 50 civilians, including singers and officers of the Kachin Independence Army (KIA), media reported, citing witnesses who said three planes carried out the attack.
The military said its forces were responding to ambushes and other attacks by the KIA and armed groups on its forces and that it met international rules of engagement.
"As security forces, they are responsible for fighting insurgents, which is essential for regional peace and stability," the military said in a statement posted on a military web site.
The KIA has been fighting on and off for six decades for greater autonomy for the Kachin people. It has voiced support for opposition to military rule in the wake of a coup last year when the generals overthrew an elected civilian government led by Nobel laureate Aung San Suu Kyi.
The shadow National Unity Government (NUG), largely made up of Suu Kyi loyalists, accused the army of targeting civilians and called on the United Nations and the international community to intervene and stop "atrocities and war crimes committed by the junta".
"We need immediate tangible action and support from the international community to hold the junta accountable," Dr Sasa, a spokesperson for the NUG set up by opponents of the junta after the coup, said in a statement.
The air strike took place in the A Nang Pa region of Hpakant township and killed at least 50 people, the BBC's Burmese-language service said, while the Kachin News Group said about 80 people had been killed and 100 were wounded.
The army described the reports as "rumours". It did not give its own estimate of the casualty toll but said only KIA members and "terrorists" were killed.
Reuters could not independently verify the figures.
The KIA said the attack targeted celebrations of the 62nd anniversary of the founding of its political wing and said the attack should be considered a war crime.
Myanmar has been trapped in a cycle of violence since the army overthrew Suu Kyi's government. Opposition movements, some armed, have emerged across the country, which the military has countered with lethal force.
Southeast Asian countries are leading efforts to bring peace to Myanmar but the junta has done little to respond to peace "consensus" agreed last year with the regional bloc Asean.
Asean foreign ministers are due to meet on Thursday to discuss the crisis. A group of 457 Myanmar civil society organisations called in an open letter for Asean leaders to scrap their five-point "consensus" and instead work with civilian leaders and the NUG.