Government spokesman Keheliya Rambukwella accused the UN of having a "hidden agenda" on Sri Lanka, where government troops finally wiped out separatist Tamil Tiger guerrillas last May after decades of ethnic bloodshed.
Rambukwella said UN Secretary-General Ban Ki-moon's appointment of a panel to advise on any violations of international human rights in Sri Lanka was "an attempt to provide oxygen to the LTTE (Liberation Tigers of Tamil Eelam)."
"The United Nations and its Secretary-General have revealed their hidden agenda in no uncertain terms," Rambukwella said in remarks posted on a government website.
Ban's latest move followed international pressure for a probe into allegations that thousands of ethnic Tamil civilians were killed by government troops in the military offensive that won the war.