Malaysian Prime Minister Mahathir Mohamad sharply criticised Myanmar leader Aung San Suu Kyi for her handling of an ethnic crisis that led to mass killings and the exodus of more than 700,000 Rohingya Muslims from her country.

Mr Mohamad said Nobel Peace Prize laureate Ms Suu Kyi was "trying to defend the indefensible" in justifying violence by Myanmar security forces against Rohingya in Rakhine state.

Hundreds of thousands of Rohingya have fled to neighbouring Bangladesh since August 2017.

"They are actually oppressing these people to the point of, well, killing them, mass killing, and burial in graves dug by the victims and that kind of thing. That may be relevant in ancient times, but in modern days, we don't do that kind of thing," said Mr Mohamad, a 93-year-old political veteran whose own past treatment of dissidents at times drew opprobrium.

Asked about the issue at a news conference on the sidelines of a summit of the Association of Southeast Asian Nations in Singapore, Mr Mohamad said that as a former political prisoner, Ms Suu Kyi should understand suffering.

It is highly unusual for leaders in the 10-nation group to publicly criticise each other.

Ms Suu Kyi became an icon for democracy after spending about 15 years under house arrest for opposing Myanmar's military dictatorship. She and her government have been widely criticised for the way they have treated the Rohingya.