A close aide to Myanmar's Aung San Suu Kyi on Wednesday dismissed mounting international pressure over alleged abuses of Rohingya Muslims as "biased and unfair", despite United Nations (UN) evidence of murder, rape and torture by security forces.

The UN has said Myanmar troops and police may have committed crimes against humanity during a four-month crackdown on the stateless minority.

Rights envoy Yanghee Lee is expected to turn up the heat next week by calling a formal 'commission of inquiry' into alleged abuses that have seen more than 70,000 Rohingya flee to Bangladesh.

Army clearance operations cut through remote villages in northern Rakhine State in retaliation for attacks by militants on police border posts in October.

Escapees have given the UN chilling accounts of babies being stabbed to death, people being burnt alive in and widespread gang rape during those operations.

The crisis has piled unprecedented pressure on Myanmar's elected government, led by Nobel laureate Aung San Suu Kyi, as it tries to emerge from the shadow of oppressive military rule.

If the UN backs a commission and its investigators find evidence that Myanmar's military has committed crimes against humanity, it could once again see Myanmar branded an international pariah.

"What Yanghee Lee is doing is not fair. It's biased," Win Htein, a close aide of Suu Kyi, told AFP. "We do not care about this kind of unfair report. Because we do not care, we do not worry."

The army's crackdown and Myanmar's continued denials that troops have acted out of turn has sapped the elation that surrounded Suu Kyi's 2015 election victory.

On Tuesday the army again defended its actions in Rakhine, using a rare press conference in Naypyidaw to insist its troops acted in accordance with the law.

Chief of the General Staff General Mya Tun Oo rejected allegations of abuse by rights groups and foreign media as "lop-sided".

A total of 76 "Bengalis" ─ a derogatory term used by many in Myanmar that implies the Rohingya are illegal immigrants from Bangladesh ─ had been killed, he said, not the hundreds alleged by the UN.

The government has created its own commission to probe the claims led by retired general turned Vice President Myint Swe.

Rights groups and the UN have dismissed it as toothless.

A member of the commission who asked not to be named said their investigations had been "thorough" and rejected the UN report alleging possible crimes against humanity as "one-sided".

The military and police have also set up separate task forces to probe the deaths of eight Rohingya in custody.

Five police were sentenced to two months detention by an internal police tribunal over a video showing them abusing Rohingya civilians, and another three senior officers have been demoted.