Sri Lanka yesterday warned that US efforts to force an international investigation into alleged war crimes on the island could have an "adverse impact" on all developing nations.
The Colombo government told the United Nations Human Rights Council (UNHRC) in Geneva that a draft resolution against Sri Lanka could set a "bad precedent".
The United States has given notice of a resolution backing UN rights chief Navi Pillay's call for an external probe into charges that Sri Lankan troops killed up to 40,000 civilians while crushing Tamil rebels in 2009.
A Sri Lankan statement to the council said the draft resolution was also a violation of its sovereignty as well as its constitution.
Dozens of pro-government women staged a demonstration outside the US embassy in Colombo, denouncing the US-led censure move at the UNHRC.
International rights groups and UN experts have said there are credible allegations that up to 40,000 Tamil civilians were killed after government forces ordered them into a no-fire zone in 2009.
The US-led resolution asks Pillay to give an oral report on progress to the council at its 27th session in September, and provide a written report by March 2015.
The draft also called on Sri Lanka to investigate allegations of military excesses and expressed "serious concern" over continuing reports of human-rights violations five years after the end of the decades-long separatist war.
The council is expected to vote on March 28 on the resolution, the third in as many years against Colombo.
At least 100,000 people were killed in the 37-year battle for a separate homeland for ethnic-minority Tamils before troops crushed the Tamil Tiger rebels.
Meanwhile officials investigating a suspected mass grave in the former northern war zone called off the digging on Friday because the 83 skeletons unearthed there seem to have been buried in an old cemetery.
Police at first suggested the Tamil Tigers could have been responsible for the burial site near a Hindu temple in the northwestern town of Mannar.
But Senerath Dissanayake, director general of the state-run Archaeological Department, said it was not a mass grave as the bodies had been "buried systematically".
"These are about 50 years old. It is a graveyard. Even our officers can identify and see the cut marks of the graves.
"We have found 83 skeletons so far and we will stop [excavation]," he said.
"We excavated up to two metres' depth. We have not started any forensic tests. That is still pending," he said, adding that the bodies had been buried in layers.
Additional reporting by Reuters