The report, released by the Australia-based Public Interest Advocacy Center (PIAC), had accused government troops of trying to destroy evidence of its crimes committed in 2008 and 2009 when it crushed the Tamil rebels fighting for a separate homeland.
"Although violations were committed by both sides, the evidentiary material indicates that members of the Sri Lankan security forces perpetrated the vast majority of alleged crimes during the investigation period," the report said.
The US has said it would table the third resolution against Sri Lanka over alleged war crimes committed by government troops during the final phase of the military battle with the LTTE.
Sri Lanka encountered similar UN resolutions both in 2012 and 2013, moved by the US and supported by India.
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The report also called for an international investigation into allegations of war crimes.
"There is nothing new in the report. We have heard them all before," military spokesman Brigadier Ruwan Wanigasooriya said.
"We want to maintain a disciplined army and we take action when we are presented with evidence," he said.
Sri Lanka has resisted repeated calls for an international probe into allegations that nearly 40,000 civilians were killed by government forces during the quarter-century civil war against the LTTE that ended in 2009.