BANGKOK >> Air strikes by Myanmar’s military killed as many as 80 people, including singers and musicians, attending an anniversary celebration of the Kachin ethnic minority’s main political organization, 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, held 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 2021 from the elected government of Aung San Suu Kyi.

Initial reports put the death toll at around 60, but later tallies raised it to about 80.

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.

The military government’s information office confirmed in a statement late Monday that there was an attack on what it described as the headquarters of the Kachin Independence Army’s 9th Brigade, calling it a “necessary operation” in response to “terrorist” acts carried out by the Kachin group.

It called reports of a high death toll “rumors,” and denied the military had bombed a concert and that singers and audience members were among the dead.

The United Nations’ office in Myanmar said in a statement that it was “deeply concerned and saddened” by reports of the air strikes.

“What would appear to be excessive and disproportionate use of force by security forces against unarmed civilians is unacceptable and those responsible must be held to account,” it said.

Envoys representing Western embassies in Myanmar, including the United States, issued a joint statement saying the attack underscores the military regime’s “disregard for its obligation to protect civilians and respect the principles and rules of international humanitarian law.”

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.

The Kachin are one of the stronger ethnic rebel groups and are capable of manufacturing some of their own armaments. They also have a loose alliance with the armed militias of the pro-democracy forces that were formed in 2021 in central Myanmar to fight army rule.

Sunday’s celebration of the 62nd anniversary of the founding of the Kachin Independence Organization, which included a concert, was held at a base also used for military training by the Kachin Independence Army, the KIO’s armed wing. It is located near Aung Bar Lay village in Hpakant township, a remote mountainous area 950 kilometers (600 miles) north of Myanmar’s biggest city, Yangon.

Hpakant is the center of the world’s biggest and most lucrative jade mining industry, from which both the government and the rebels derive revenue.

As many as 80 people were killed and about 100 were injured in Sunday’s attack on the first day of a three-day celebration of the KIO’s founding, a spokesperson for the Kachin Artists Association told The Associated Press by phone. He said he first heard there had been 60 deaths, but was later told by sources close to Kachin Independence Army officials that about 80 people had died.

He said military aircraft dropped four bombs on the celebration at about 8 p.m., according to members of his group who were there. Between 300 and 500 people were in attendance and a Kachin singer and keyboard player were among the dead, said the spokesperson, who asked not to be identified because he feared punishment by the authorities.

Those killed also included Kachin officers and soldiers, musicians, jade mining business owners and other civilians, he said. They also included at least 10 Kachin military and business VIPs sitting in front of the stage, and cooks working backstage, he added.

The Kachin News Group, a media outlet sympathetic to the KIO, reported that an initial search found 58 bodies and that government security forces had blocked the wounded from being treated at hospitals in nearby towns. It reported later that more than 20 more bodies had been recovered, bringing the death toll to about 80.

Col. Naw Bu, a spokesperson for the Kachin Independence Army, said by phone that KIA soldiers, musicians, businesspeople and villagers were among the dead, but he could not confirm a casualty number due to communications problems. He said the deaths were a loss for all Kachin people, and its group would fly the Kachin flag at half-staff.

An emergency services rescue worker who was in Hpakant and also asked for anonymity said he saw three military aircraft making bombing runs over the celebration ground, just a few kilometers (miles) away. He said he was barred by the KIO from entering the area but heard that more than 60 people were killed, including a KIA brigade commander.

The Assistance Association for Political Prisoners, a non-governmental organization that tracks killings and arrests, said Friday that 2,377 civilians have died in crackdowns by the security forces since the army took power. Its figure, however, does not always include people killed in military actions in the countryside.

“We fear this attack is part of a pattern of unlawful aerial attacks by the military which has killed and injured civilians in areas controlled by armed groups,” Amnesty International’s deputy regional director, Hana Young, said in a statement.

“The military has shown ruthless disregard for civilian lives in its escalating campaign against opponents. It is difficult to believe the military did not know of a significant civilian presence at the site of this attack. The military must immediately grant access to medics and humanitarian assistance to those affected by these air strikes and other civilians in need,” Young said.

Cambodia, the current chair of the Association of Southeast Asia Nations, said Sunday that the group’s foreign ministers will hold a special meeting in Indonesia this week to consider the peace process for Myanmar. Myanmar’s generals have all but shunned the group’s previous efforts.

“As officials and leaders from the Association of Southeast Asian Nations prepare to host high-level meetings in the coming weeks, this attack highlights the need to overhaul the approach to the crisis in Myanmar,” Amnesty International said. “ASEAN has to step up and formulate a more robust course of action so that military leaders end this escalating repression.”