A Myanmar military report that said no Rohingya civilians were killed during a months-long crackdown is "absurd" and the International Criminal Court must now launch its own investigation, a human rights group said.

Myanmar's army released a report late on Monday that found "no deaths of innocent people" after deadly attacks by Rohingya rebels on several police posts in northern Rakhine state on August 25 sparked a brutal military campaign.

The army said 376 "terrorists" were killed in fighting after the August attacks. The crackdown led to the mass exodus of about 600,000 Rohingya civilians who fled the predominantly Buddhist country into neighbouring Bangladesh.

Many survivors in squalid camps inside Bangladesh - described as the world's worst refugee crisis - have reported mass killings, torture, and rape against Rohingya children, women, and men.

{articleGUID}

"The Burmese military's absurd effort to absolve itself of mass atrocities underscores why an independent international investigation is needed to establish the facts and identify those responsible," said Human Rights Watch's Brad Adams in a statement on Tuesday.

"The Burmese authorities have once again shown that they can't and won't credibly investigate themselves."

The United Nations has called the majority-Muslim Rohingya in Myanmar the world's most persecuted minority.

Jeremy Laurence, a UN spokesman, told a news conference on Tuesday their investigators in Bangladesh found ample evidence of the killing and torture of civilians in Myanmar.

"Our findings are quite clear on what is happening," Laurence said. "What we found took place in Rakhine state… is a textbook example of ethnic cleansing, murder, rape, assault, killings, torture. We heard [this] from people… over and over again."

Human Rights Watch said it is time for the International Criminal Court in The Hague to investigate Myanmar's authorities.

{articleGUID}

"The military's grave crimes committed with impunity are exactly what the International Criminal Court was created for," Adams said.

The Myanmar military's report and its denunciation by Human Rights Watch came as US Secretary of State Rex Tillerson arrives in Myanmar on Wednesday.

Demands have been growing in the United States for Washington to impose economic and travel sanctions against the military and entities under its control over the Rohingya crisis.

US President Donald Trump said on Tuesday he backed the "safe and voluntary return" of the refugees.

"The United States supports efforts to end the violence, to ensure accountability for atrocities committed," a White House statement quoted the president as saying. "We welcome the commitments by the government of Myanmar and we are ready to support the implementation of the Rakhine recommendations."