The UN rights chief called Tuesday for a fresh international investigation into Myanmar's abuses against its Rohingya Muslim minority, warning of possible "elements of genocide" in the violence.

Speaking before a special session of the UN Human Rights Council on abuses against the Rohingya, Zeid Ra'ad Al Hussein condemned "widespread, systematic and shockingly brutal" attacks, as well as decades of discrimination and persecution.

An army-led crackdown has forced some 620,000 people to flee from northern Rakhine state and across the border into squalid camps in Bangladesh in recent months, leaving hundreds of villages burned to the ground.

Myanmar's military denies accusations by the UN and US that it has committed ethnic cleansing against the Rohingya.

But Zeid condemned policies that have left the minority wallowing in statelessness for decades, along with dehumanising discrimination and segregation.

He described horrific violence and abuse, including allegations of "killing by random firing of bullets, use of grenades, shooting at close range, stabbings, beatings to death and the burning of houses with families inside". 

He also pointed to "serious bodily or mental harm inflicted on Rohingyas, including children", including torture and rape, forced displacement and the "systematic destruction of villages".

"Given all of this, can anyone rule out that elements of genocide may be present?" Zeid asked the 47-member council.

He called on the UN General Assembly to launch a new "impartial and independent mechanism", to work alongside a fact-finding mission already dispatched by his office.

In March the rights council approved the fact-finding mission to investigate alleged crimes by security forces, particularly in Rakhine.

But Myanmar has so far refused to cooperate and has blocked access to the team of investigators, who have begun their work from outside the country