The US will support efforts to get Sri Lanka to implement a government commission's conclusions in relation to the civil war, officials say.
They say the US will back a resolution in the UN Human Rights Council in March which urges Colombo to look into war crimes allegations by its forces.
Both Tamil Tiger rebels and the army have been accused of abuses during the final phase of the war in 2009.
Sri Lanka appointed the commission to examine possible rights violations.
It did so after a separate 2010 report written for the UN found that war crimes allegations were credible and warranted a full investigation.
The Sri Lankan Lessons Learnt and Reconciliation Commission (LLRC) cleared the military of allegations that it deliberately attacked civilians and deprived them of food and medicine as a tactic of war.
It said that there were some violations by troops, but only at an individual level.
The UN report reached a different conclusion: It said that allegations of rights violations were "credible" on both sides.
Maria Otero, the most senior US official to visit Sri Lanka since 2005, said she discussed the recommendations made by the LLRC with President Mahinda Rajapaksa on Monday.
She said that although the LLRC had addressed a "number of crucial areas", there were "shortcomings on accountability".
"The US will support a resolution in the UN Human Rights Council in March that provides an opportunity for the government of Sri Lanka to describe what it intends to do to implement the LLRC's recommendations and advance reconciliation, as well as address accountability, human rights and democracy concerns," she said.
Human rights groups estimate that up to 40,000 civilians were killed in the final months of the war.