The government in Colombo has faced repeated calls for a probe from Western countries and rights groups ever since it launched a final offensive to crush Tamil Tiger separatist rebels in the country's northeast in early 2009.
The assault brought an end to a 37-year-old ethnic conflict that had claimed 100,000 lives since 1972, but hurt the reputation of the country abroad amid criticism of the conduct and tactics of government forces.
The UN estimates that 7,000 civilians perished during the first four months of last year, though this figure is disputed by the government.
On Thursday, UN human rights envoy Philip Alston concluded that video footage said to be of Sri Lankan troops executing unarmed Tamil Tiger rebels last year was authentic and urged Colombo to accept a war crimes probe.
Reacting on Friday, Sri Lankan Human Rights Minister Mahinda Samarasinghe again dismissed the video as a fraud and accused Alston of leading a personal crusade against the country.
"Philip Alston