Ethnic minority Karen insurgents attacked a Myanmar army outpost near the Thai border on Tuesday in some of the most intense clashes since a military coup nearly three months ago threw the country into crisis.

The Karen National Union (KNU), Myanmar’s oldest rebel force, said it had captured the army camp on the west bank of the Salween river, which forms the border with Thailand. The Myanmar military later hit back against the insurgents with air strikes, the KNU and Thai authorities said.

The fighting took place as the junta, in a setback for diplomatic efforts by the Association of Southeast Asian Nations (Asean), said it would “positively” consider the bloc’s suggestions to end the turmoil in Myanmar but only when stability was restored.

The Asean leaders said after meeting on the weekend with the junta chief that they had reached a consensus on steps to end violence and promote dialogue between the rival Myanmar sides.

The outbreak of hostilities near the border shifted the focus of opposition to the junta away from the pro-democracy protests that have taken place in cities and towns across the country since the coup on February 1. The military overthrew the elected government of Aung San Suu Kyi, detained leaders and then cracked down with lethal force on anti-coup protesters.