The Russians have promised not to deploy any more troops in Kosovo until a deal on Moscow's role in the province's peacekeeping force is reached, according to the US special envoy Strobe Talbott, currently in the Russian capital.

Later on Sunday President Clinton is due to speak by phone to Boris Yeltsin.

Mike Williams in Pristina: "Russians making a political point"

And in the Kosovo capital, Pristina, Nato commanders are still trying to reach agreement with a 200-strong Russian force controlling the city's airfield.

Lieutenant-General Mike Jackson, head of the K-For peacekeeping force, intends to set up his headquarters there, but so far British troops have been allowed only partial use of the airfield.

The Itar-Tass news agency said he and the newly-promoted Russian commander, Colonel-General Viktor Zavarzin, held "goodwill" talks on ways of jointly using the airfield.

An explanation by foreign minister Igor Ivanov that the Russian troop deployment had been a mistake and would be reversed has not been matched by action on the ground.

Mr Talbott made his comments at the Russian Foreign Ministry on Sunday, before concluding talks with Mr Ivanov. He added that Russia's role in the force in some parts of Kosovo would be "important and manifest", but ruled out partition of Serbia's southern province.

More troops are expected to pour into Kosovo from Macedonia and Albania during the next few hours as K-for continues its task of making the province safe for the return of hundreds of thousands of refugees.

Nato leaders have been playing down the tension caused by the Russian presence.

President Clinton said: "We look forward to working with Russia and others who may not have agreed with our military campaign but do agree with the proposition that all the people of that tiny land - Serb and Albanian alike - should be able to live in peace and freedom."

Andrew Harding in Moscow: "Confusion over who is running Russian policy"

But so far the United States is believed to have resisted any modification to the UN-backed formula for peacekeeping in Kosovo.

UK troops - the largest part of the Nato-led force - were welcomed as liberators by Kosovo's Albanians as they swept up the main road to Pristina from Macedonia at the beginning of Operation Joint Guardian.

Promise to all Kosovans

General Jackson said Nato was in the "first stages of what is still a complex operation," but pledged to "provide a secure environment for all the people of Kosovo, whatever their ethnic background."

(Click here to see an animated map showing timetable of Serb withdrawal and Nato's planned movements)

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The BBC's Ben Brown: Ecstatic crowds greeted the troops

A total of 1,500 UK soldiers crossed the border from the former Yugoslav Republic of Macedonia in the first wave. Troops from the other Nato countries contibuting to K-For - France, Italy, Germany and the United States - also entered Kosovo later.

The multi-national force will eventually number around 50,000.

The soldiers' first task was to secure the hillsides and the main road leading north to Pristina.

The French contingent was held up by a minefield, apparently planted by the retreating Yugoslav army.

The UK soldiers faced no major obstacles as they advanced towards Pristina.

In one minor delay, Yugoslav army officers manning a checkpoint on the main road said they needed more time to retreat from their positions.

Nato forces did not compromise, and the Yugoslavs let them proceed after about 30 minutes.

Earlier, UK soldiers came across more than 30 Serb military and paramilitary troops, and disarmed them.

Albanians celebrate, Serbs flee

The deployment is one of the biggest military operations in Europe since World War II.

It is intended to help thousands of Kosovo Albanian refugees return home, though they have been warned they will have to wait until the province is made safe.

There were scenes of celebration in the refugee camps in the Former Yugoslav Republic of Macedonia as the Nato forces moved into Kosovo.

Several thousand Serbian refugees are reported to have arrived in Montenegro, after fleeing Kosovo.

Many Serbs in the province feel that Nato cannot guarantee their safety after the withdrawal of Yugoslav forces.

• Russian troops camp in Pristina
• The push into Kosovo in pictures
• UK leads Nato into Kosovo
• Flying into Kosovo
• Kosovo Serbs pack up and leave