Leaked U.S. documents say American diplomats accused top Sri Lankan officials, including President Mahinda Rajapaksa, of playing a role in last year's alleged massacre of Tamil Tiger rebels.
The classified diplomatic cable sent last January by the U.S. Embassy in Colombo is one of thousands the website WikiLeaks made public this week.
In the cable, U.S. officials wrote that the Sri Lankan government showed no signs of investigating alleged human rights violations committed by its side in the closing months of a 25-year-old civil war between the rebels and government.
The officials say any effort to investigate is further complicated because President Rajapaksa, his brothers and opposition candidate, former army commander Sarath Fonseka, are responsible for many of the alleged crimes.
Sri Lankan forces defeated the Tamil Tigers in May of last year, ending their decades-long campaign for an independent state.
The United Nations says at least 7,000 ethnic Tamil civilians were killed in the last months of fighting.
Human rights groups have accused both the Tigers and government forces of human rights violations during the conflict.
Sri Lanka denied its troops committed war crimes and has rejected a U.N. probe into the fighting.
On Thursday, a British group canceled a planned speech by President Rajapaksa after his visit raised security concerns.
The Oxford Union was scheduled to host the speech by Mr. Rajapaksa, who arrived in Britain for a visit Monday. Sri Lanka's minority Tamil group had planned to protest the address.
Mr. Rajapaksa said he is sorry the speech had to be canceled, but that he will continue to seek places to talk about his "future vision for Sri Lanka."
The Oxford Union released a statement Wednesday saying its decision was not related to Mr. Rajapaksa's political positions.