Asean is gravely concerned about an escalation of violence in Myanmar and is calling for restraint and an immediate cessation of fighting, the bloc's chair Cambodia said.

Myanmar has been trapped in a cycle of violence since the army ousted Nobel laureate Aung San Suu Kyi's elected government in February 2021, detaining her and thousands of activists and launching a brutal crackdown that has given rise to armed resistance movements.

Recent weeks have seen some of the bloodiest incidents, with dozens killed.

In a statement, the Asean chair cited the bombing of Myanmar's largest prison, conflict in Karen state and an air strike in Kachin state on Sunday, which is reported to have killed at least 50 people.

"We are deeply saddened by the growing casualties, and the immense suffering that ordinary people in Myanmar have endured," said the statement.

The conflict was not only exacerbating the humanitarian situation but was also undermining efforts to implement a peace "consensus" agreed between Asean and the junta last year, said the statement.

"We, therefore, strongly urge utmost restraint and immediate cessation to violence," said the statement, which called for all parties to pursue dialogue.

Asean is leading diplomatic efforts to bring peace to Myanmar but the junta has done little to implement the "consensus", which committed to an immediate halt to violence and the start of dialogue towards a peace agreement.

Asean foreign ministers are due to meet on Thursday to discuss the crisis, Cambodia said on Sunday.

A group of 457 Myanmar civil society organisations have called in an open letter for Asean leaders to scrap the peace plan it agreed with the military and instead work with civilian leaders and a shadow government.

- Reuters