The top United Nations human rights official called on Friday for allegations of atrocities committed against the Muslim Rohingya minority in Myanmar to be referred to the International Criminal Court (ICC) for prosecution.

Zeid Ra'ad al-Hussein, UN High Commissioner for Human Rights, also urged Myanmar's government to allow monitors into northern Rakhine state to investigate what he called suspected "acts of genocide" against the Muslim minority.

"What we're saying is...there are strong suspicions, yes, that acts of genocide may well have taken place. But only a court, having heard all the arguments, will confirm this," Zeid told a news conference.

"It wouldn't surprise me in the least if a court would make that finding in the future," he said.

The United Nations defines genocide as acts meant to destroy a national, ethnic, racial or religious group in whole or in part. Such a designation is rare under international law, and Zeid noted that the threshold is high.

Nearly 700,000 Rohingyas have fled Rakhine state into Bangladesh since insurgent attacks sparked a security crackdown in August. Many have provided harrowing testimonies of executions and rapes of civilians by Myanmar security forces.

Myanmar wants to see clear evidence to support accusations of ethnic cleansing or genocide, National Security Adviser Thaung Tun said on Thursday.

Zeid, asked about the remarks, said that Myanmar authorities were "serial deniers of the truth", adding: "To suggest that nothing serious has happened in Rakhine, I mean it's preposterous, ridiculous. How can they say such a thing?"

Myanmar has not allowed Yanghee Lee, the UN investigator on human rights in Myanmar, to visit the country to investigate.

She said on Friday she was "increasingly of the opinion that the events bear the hallmarks of genocide" and said she would press for prosecutions for crimes committed against entire ethnic and religious groups.

"The government leadership who did nothing to intervene, stop, or condemn these acts must also be held accountable," Lee said in a report based on her interviews with survivors in Bangladesh.