The Geneva-based UN Human Rights Council has set up multiple investigations and fact-finding missions into major trouble spots, including an active one for Myanmar.
But some have expressed concern over the limitations of those probes, which focus on gathering a broad range of evidence about alleged atrocities, rather than assembling specific legal cases against individuals that can be taken to court.
In the Syrian case, the UN General Assembly voted in 2016 to set up an "independent and impartial mechanism" to prepare prosecutorial files.
UN rights chief Zeid Ra'ad Al Hussein said Wednesday that a similar body was needed for Myanmar, where senior UN officials have said the military is continuing to wage a campaign against the Rohingya Muslim ethnic group that amounts to "ethnic cleansing".
Zeid called on the rights council to "ask the General Assembly to establish a new independent and impartial mechanism to prepare and expedite criminal proceedings in courts."
In his annual report to the council, Zeid restated his concern that "acts of genocide may have taken place" in the Rohingya homeland of Rakhine state.
An estimated 700,000 Rohingya have fled over the border to Bangladesh since an army crackdown was launched in Rakhine in August.
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