Rights group Amnesty International says the actions of Myanmar’s military may constitute “crimes against humanity” after allegations of violence against the Rohingya Muslim minority.
Its report accuses Burmese forces of murdering civilians, rape and torture.
Myanmar’s military has denied accounts of atrocities and says it is conducting anti-terrorist raids in Rakhine.
At a meeting of regional leaders in Yangon, the government said it needed “time and space” to resolve the issue.
Malaysia said this was now a “regional concern”, and called for the Association of South East Asian Nations (Asean) to co-ordinate humanitarian aid and investigate the allegations.
It is extremely rare for the 10-nation regional body to discuss the affairs of a member country.