Despite Sri Lanka’s vehement objections, the United Nations Secretary General Ban Ki-Moon has appointed a trio of international experts to examine reports of widespread war crimes during Sri Lanka’s war against the Liberation Tigers.

Although UN spokesman Martin Nesirky emphasised the panel had a mostly consultative role and that "primary responsibility for investigating rests with the authorities of Sri Lanka," many diplomats in Colombo see the move as a precursor to a full-blown war crimes investigation, AFP reported.

Sri Lanka responded with fury to the UN announcement, vowing to deny the experts access and rejecting the accusations by the Tamils and international human rights organizations.

Sri Lanka accused the UN of a "hidden agenda" behind its plans to investigate reports of atrocities by soldiers in the final months of the island's savage civil war, and has encouraged Sinhala protests outside the UN offices in Colombo.

The head of the UN panel, Marzuki Darusman, a former Indonesian attorney general, has in turn criticised Colombo's decision to ban him and colleagues from the country.

"Everybody loses out if we cannot go to Sri Lanka, it will make it harder for the truth to be unearthed," Mr. Darusman told the BBC, describing the ban as "most unfortunate".

His remarks came after Sri Lanka's External Affairs minister, Prof. Gamini Lakshman Peiris, said Colombo would not grant visas to members of the panel, which he described as "totally unnecessary".

The United States backed the UN move and urged Sri Lanka to cooperate. But Russia, also a permanent UN Security Council member, raised concerns about the appointment of the panel in the first place.

“The United States supports a robust accountability process that will provide a durable foundation for national reconciliation and the rule of law in the aftermath of Sri Lanka’s decades-long conflict,” US Permanent Representative to the United Nations, Susan Rice said.

“The government of Sri Lanka should give serious consideration to its Commission’s recommendations. We strongly urge the Government of Sri Lanka to take advantage of this UN Panel’s expertise,” she added.

The other two members of the UN panel are human rights expert Yasmin Sooka from South Africa and Steven Ratner, an expert in international law of war from the United States. Mr. Ban launched the investigation "to advise him on the issue of accountability with regards to any alleged violations of international human rights and humanitarian law during the final stages of the conflict in Sri Lanka."

The panel will have support staff, to be based in New York, press reports filed by reporters based in the UN’s headquarters said.

Ms. Sooka joined the Foundation for Human Rights in 2001 and serves as its Executive Director. She practised as a human rights lawyer during the apartheid era. In 1995, she was appointed as a Commissioner on the Truth and Reconciliation Commission and was responsible for the final report.

Prof Steven Ratner is a Professor of Law at University of Michigan Law School and in 1998-99, was appointed by the UN Secretary-General to a three-person group of experts to consider options for bringing the Khmer Rouge to justice.

Apart from heading the UN panel on Sri Lanka, Mr. Darusman is also the UN's special rights investigator for North Korea.

According to the BBC, Mr. Darusman was part of an international team appointed to observe proceedings on a previous Sri Lankan commission on atrocities - but he and other members of the International Independent Group of Eminent Persons (IIGEP) resigned saying that commission did not meet basic minimum standards.

In rejecting international investigations, Sri Lanka claims its own panel, set up earlier this year to look into the ‘causes of terrorism’ in Sri Lanka, is adequate.

Peggy Hicks, global advocacy director with Human Rights Watch, warned it has "long been abundantly clear that the Sri Lankan government is unwilling to seriously investigate wartime abuses."

"Secretary-General Ban's new panel will only be of value if it can quickly produce a roadmap for an independent investigation that the secretary-general implements," she told AFP.

On Monday, monks and lay members of a Buddhist nationalist party protested outside the UN offices in Colombo.

"The UN has no right, authority or mandate to appoint a committee. It's an interference with Sri Lankan affairs," party leader Rev. Omalpe Sobitha told the gathering. "The UN is acting as an agent of terrorism."

Ban Ki-moon's appointment of the panel was "an attempt to provide oxygen" to the defeated Tamil Tigers, Sri Lankan government spokesman Keheliya Rambukwella has also said.

The International Crisis Group said last month the Sri Lankan government had killed thousands of its civilians by shelling "no-fire zones" in the last months of the war.

The ICG said the military encouraged hundreds of thousands of Tamil civilians to move into government-declared "no-fire zones" and then subjected them to "repeated and increasingly intense artillery and mortar barrages."

"This continued through May despite the government and security forces knowing the size and location of the civilian population and scale of civilian casualties," the ICG reported.

The group said it had collected eyewitness statements as well as hundreds of photographs, videos, satellite images, electronic communications and documents from multiple sources to support the charges.