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PRISTINA, Yugoslavia (CNN) -- The first group of what should become a 2,000-strong force of international peace accord "verifiers" have arrived in Kosovo, officials said Saturday.

The 11 Britons with military backgrounds arrived in Kosovo's provincial capital of Pristina Friday evening.

Initially, they will join the British team in the Kosovo Diplomatic Observer Mission until the new international Kosovo Verifying Mission (KVM) is established under the auspices of Europe's main security body, the Organization for Security and Cooperation in Europe.

"Technically these are the first verifiers," said Duncan Bullivant, spokesman for the 54-nation OSCE.

Another 50 British verifiers are due in Kosovo by the end of next week, and 76 U.S. verifiers are in Belgrade and are expected in Pristina soon. Others will join them from France and elsewhere.

Bullivant said the KVM was expected to be up and running by the end of the month.

The OSCE mission was set up last month under an agreement between Yugoslav President Slobodan Milosevic and U.S. Balkans envoy Richard Holbrooke.

Milosevic agreed to the mission after he narrowly met NATO demands for a significant Yugoslav troop withdrawal from Kosovo, where his forces had cracked down hard on separatist Kosovo Liberation Army rebels, who are ethnic Albanians, and their alleged supporters.

The OSCE force is to verify that both Yugoslav forces and KLA separatists fighting for an independent Kosovo do not re-launch their military campaigns.

But with no political deal yet in place between Milosevic and the KLA, the verifiers, who will not be armed, will be working in difficult circumstances.

Those difficulties were again highlighted when Serbian media reported Saturday that five suspected ethnic Albanian KLA rebels had died Friday in a shootout with Serbian police.

The Serbian-run Media Center in Pristina said a search operation was under way for missing Serbians believed involved in the shootout.

U.S. special envoy for Kosovo, Ambassador Christopher Hill, held a rare meeting with top KLA leaders on Friday in an effort to convince them to join the search for a political settlement.

The KLA did not sign the latest Holbrooke-Milosevic accord on Kosovo.

There was also tension Saturday between the United Nations and Belgrade, as Yugoslav authorities continued to bar U.N. war-crimes investigators into Kosovo.

Belgrade has barred Louise Arbour, chief prosecutor for the International War Crimes Tribunal on the former Yugoslavia, and her team of investigators from traveling into the province.

A statement by the Yugoslav justice ministry, published by local news agencies Saturday, said the conflict in Kosovo was Yugoslavia's internal affair and is outside the tribunal's jurisdiction.

Arbour had planned to follow up "specific and credible" allegations of Serbian atrocities against ethnic Albanian civilians, including reports of summary executions.

Ethnic Albanians normally comprise about 90 percent of Kosovo's population, although many residents have fled the area because of the fighting.

The Associated Press and Reuters contributed to this report.