Updated

U.S. senators John McCain and Lindsey Graham on Wednesday accused the Obama administration of overlooking alleged war crimes by the regime of Syrian President Bashar al-Assad in a rush to bring the war-torn nation’s leader to peace negotiations.

A new report issued earlier in the day by three international war crimes prosecutors claims that the Syrian government is behind the "systematic killing" of approximately 11,000 detainees between March 2011 and August 2013.

“The Obama Administration has ignored countless acts of brutality carried out by the Syrian government and refused to hold President Assad accountable for his relentless assault against the Syrian people,” said McCain, R-Ariz., and Graham, R-S.C., in a joint statement. “In trying to make Syria an issue of chemical arms control, we have tacitly allowed for the continued use of conventional weapons, and turned a blind eye to the unprecedented level of violence committed against civilians in Syria.”

The 31-page report was commissioned by a London-based law firm operating on behalf of the government of Qatar, which has financed and armed rebel groups in Syria and repeatedly called for Assad to stand trial for war crimes. Two of the report's authors, Sir Desmond de Silva and David Crane, argued war crimes cases related to the 1991-2002 civil war in Sierra Leone, while the third author, Sir Geoffrey Nice, led the prosecution of former Serbian leader Slobodan Milosevic at The Hague.

The publication of the report is believed to be timed to coincide with this week's peace conference in Geneva, which has been convened with the hope of creating a transitional government.

British Foreign Secretary William Hague called the report "further evidence of the systematic violence and brutality being visited upon the people of Syria by the Assad regime. We will continue to press for action on all human rights violations in Syria, and for accountability for those who perpetrate them."

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The Associated Press contributed to this report.