Details of the UN mission were sketchy. Spokesman Fred Eckhard said only that the UN chief would be sending a mission to the region ``in the coming days.''

The Security Council last week asked Secretary-General Kofi Annan for such a mission, to enable the United Nations to have a first-hand account of the situation on the ground. Since a Serb crackdown on ethnic Albanians began in February, the United Nations has relied on other organisations for information on the conflict. Only UN humanitarian workers are in Kosovo.

The UN mission would be in addition to the 2,000-member verification team agreed to in marathon talks between US envoy Richard Holbrooke and Yugoslav President Slobodan Milosevic that came amid threatened NATO attacks.

Milosevic agreedon Monday to withdraw his forces from Kosovo, begin peace negotiations with separatist ethnic Albanians and allow a team into Kosovo to verify Serb compliance with UN demands.

Russia's UN ambassador, Sergey Lavrov -- whose country had opposed NATO intervention -- said on Tuesday that the agreement ``proves that ambassador Holbrooke's determination to find a diplomatic solution with the support of the contact group was stronger than the threat of force.''

Deputy US Ambassador Peter Burleigh said the Security Council would probably adopt a resolution backing the agreement giving it the force of international law.

He noted that the contact group of states, which has been meeting regularly on Kosovo, had said last week that there would ``probably be a Security Council resolution with regard to the verification agreement.''

No text of a resolution, however, has begun circulating, Council diplomats said.

``The key is compliance with all of the aspects of the Security Council resolution 1199,'' ofSeptember 23, Burleigh said.

The Serb crackdown, launched on Februsry 28, was aimed at crushing the Kosovo Liberation Army, fighting for independence of the majority Albanian province, which is part of the Yugoslav republic of Serbia.

Hundreds have been killed in Kosovo and hundreds of thousands more have been forced from their homes during the seven-month operation in Kosovo, which is 90 percent ethnic Albanian.

The UN high commissioner for refugees welcomed the report of a breakthrough in principle. The main humanitarian agency on the ground in Kosovo hopes the agreement ``will contribute rapidly to reducing the level fear which is currently impeding so many displace people from returning home,'' Eckhard said.