Myanmar’s junta defended its air strikes on a concert, organized by an ethnic minority group, that killed at least 60 people, an act opponents have described as a possible war crime at a time of deepening conflict in the Southeast Asian nation.

Sunday’s aerial attack in Kachin State killed concert performers along with civilians and militia officers and is seen as one of the deadliest since the junta overthrew the civilian government in a coup last year. The strikes appeared to target a concert at a base used for military training by the armed wing of the Kachin Independence Organization, which is aligned with forces loyal to detained civilian leader Aung San Suu Kyi.

While opposition and rights groups have called the attack a likely war violation, the junta argued it carried out the strikes in response to attacks on its forces and this was in line with international rules of engagement.