A Sri Lanka Cabinet minister began a "fast unto death" outside the United Nations compound in Colombo on Thursday to demand that the organization stop its investigation into alleged war crimes.

Wimal Weerawansa, the construction minister, told reporters he would fast until U.N. Secretary General Ban Ki-moon dissolves a panel made up of an Indonesian, a South African and an American.

Ban appointed the three-member panel to advise him on violation of human rights and related issues when Tamil Tiger rebels were militarily defeated in May last year. The move is prelude to a war crimes inquiry.

The United Nations has been concerned about accountability issues related to the military defeat of the rebels, including alleged war crimes by troops and rebels -- allegations that both parties deny.

"Ban's move is intended to bring President Mahinda Rajapaksa before a war crimes tribunal. We will not allow that to happen," Weerawansa told a news conference earlier in the week.

Nearly a hundred of Weerawansa supporters gathered Thursday morning outside the U.N. compound. The entrance to the complex was open, however, as some staff went about their work.

In New York, the U.N. associate spokesman Farhan Haq said Ban's chief of staff, Vijay Nambiar, met with Sri Lanka's ambassador to the United Nations, Palitha Kohona, who gave "full and clear" assurances of U.N. staff safety and security.

He added that Weerawansa said U.N. staff would be allowed to move in and out of the compound.

"We trust that the government of Sri Lanka will honor the commitments made in ensuring the safety and security of our staff so that they can continue the vital work being carried out by the United Nations each day to help the people of Sri Lanka," Haq told reporters in New York.

The U.N. Country Team (UNCT) confirmed that essential staff will return to normal work starting Friday.

"However, as there are some indications of demonstrators remaining outside the compound, the UNCT will assess whether all staff could return soon," Haq said.

Opposition leader Ranil Wickremasing urged the government to make a statement on how a minister ended up staging demonstrations.

"Today, Sri Lanka is on the verge of being labeled as an international fugitive facing the risk of being hauled up before the International Criminal Court," Rajapaksa's one time foreign minister and now an opposition MP, Mangala Samaraweera, told parliament.

The two English morning national newspapers also criticized the move.

The Daily Mirror said in an editorial "after all this drama the government issued one of its silliest statements ever" justifying the siege as a "peaceful demonstration."

The Island newspaper said Weerawansa and his supporters "must be condemned unreservedly for their abortive bid to hold U.N. staff incommunicado."