The government of President Mahinda Rajapakse formally rejected the demand by rights chief Navi Pillay for an external investigation into what she called "credible allegations" that 40,000 ethnic Tamil civilians were killed by Sri Lankan forces in 2009.
Pillay's recommendation to a UN Human Rights Council (UNHRC) meeting in Geneva next month "reflects bias and is tantamount to an unwarranted interference in the internal affairs of a sovereign state", Colombo said in a statement.
The United States has already said it will move a third censure motion against Sri Lanka at the UNHRC, buttressing the recommendations of Pillay who visited Sri Lanka on a week-long fact-finding mission last August.
Shortly before leaving the island, she launched a scathing attack on Sri Lanka's failure to deliver on promises to ensure accountability and accused the Rajapakse regime of becoming "increasingly authoritarian".
Sri Lanka's latest criticism of the UN official, set out in a 23-page statement, accused