US Secretary of State Hillary Clinton has given her backing to a Sri Lankan panel on post-war reconciliation.
Mrs Clinton said the probe "holds promise" but insisted it should be able to investigate war crimes.
Sri Lankan Foreign Minister GL Peiris, who met Mrs Clinton in Washington, said the panel might involve the UN "along the road... if there is a need".
Sri Lanka's 37-year conflict with the Tamil Tigers ended last year. The UN estimates 100,000 people were killed.
'Independent and impartial'
Mrs Clinton said: "I think this commission holds promise and we hope and expect that it will fulfil that promise.
"We expect that the mandate will enable them to fully investigate serious allegations of violations," she said.
Mrs Clinton said the panel should be "independent, impartial and competent".
Mr Peiris urged the international community to let the panel do its work "without hindrance".
He added: "If you feel that there is a need for support, then we certainly will be happy to engage in a dialogue with the United Nations."
The BBC's Charles Haviland in Colombo says that for several weeks there have been heated exchanges between the Sri Lankan government, which denies that its forces were excessively heavy-handed in defeating the Tamil Tiger rebels last year, and a series of international campaigning groups which allege that they were, even that they may have committed war crimes.
Amnesty International has been highly critical of Sri Lanka in the aftermath of the war.
Its secretary general Claudio Cordone said last week: "One would be hard pressed to imagine a more complete failure to hold to account those who abuse human rights."