A five-minute video authenticated by a UN expert panel shows bound and blindfolded men being shot by uniformed soldiers.
The grainy video also shows soldiers mocking naked male and female corpses lying on a dirt track.
The UN's expert on extra judicial executions, Christof Heyns, told The Associated Press on Tuesday that the footage provides prima facie evidence of war crimes committed by the Sri Lankan army.
He says the video should now be used to initiate legal proceedings against those responsible. The Sri Lankan government denies the footage is authentic.
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