Former U.N. chief Ban Ki-moon called on his successor on Monday to engage directly with Myanmar’s military to ward off an increase in post-coup violence, saying southeast Asian countries should not dismiss the turmoil as an internal issue for Myanmar.

U.N. Secretary-General Antonio Guterres’ special envoy on Myanmar, Christine Schraner Burgener, has communicated with the military since it toppled an elected cabinet led by Aung San Suu Kyi on Feb. 1, but the army has not allowed her to visit.

“Given the gravity and urgency of the situation, I believe the secretary-general himself should use his good offices to engage directly with the Myanmar military, to prevent an escalation of violence,” Ban, secretary-general from 2007 to 2016, told a U.N. Security Council meeting.

Guterres is “very actively involved” on Myanmar and “has been for a long time,” said U.N. spokesman Stephane Dujarric, adding: “His good offices, along with his special envoy, are always available. We all want to see an end to the violence.”

Guterres told the Security Council on Monday that a “robust international response grounded on a unified regional effort” was needed, calling on “regional actors to leverage their influence to prevent further deterioration and, ultimately, find a peaceful way out of this catastrophe.”

The 10-member Association of Southeast Asian Nations (ASEAN) has been trying to find a way out of the violence tearing at fellow member Myanmar. Junta chief Min Aung Hlaing is set to attend an ASEAN summit in Indonesia on April 24.

Ban, a former South Korean foreign minister who is now a member of The Elders global leaders group, said “ASEAN must make it clear to the Myanmar military that the current situation is so grave that it cannot be regarded only as an internal matter.”

737 people have been killed by security forces since the coup and 3,229 remain in detention, according to the Assistance Association for Political Prisoners activist group.

“The military’s use of lethal force and the gross violations of human rights being perpetrated against the civilians are not compatible with the ASEAN Charter,” he said. “These actions are clear violations of international law, and constitute a threat to the peace, security and stability of the region.”

Ban also called on the Security Council to move beyond statements to collective action. Nonetheless, some diplomats say China and Russia are likely to prevent any stronger action.