For three hours after dawn, wave after wave of helicopters ferried about 1,500 British troops across the border from the former Yugoslav Republic of Macedonia.

But they were not the first foreign troops to enter Kosovo. Hours earlier, a contingent of Russian soldiers made an unexpected advance into the regional capital, Pristina.

Russian troops: Mobbed in Pristina

The Russian troops were given a heroes' welcome by cheering crowds of Serbs when they arrived in the town.

The task of the advancing Nato troops is to secure the hillsides and the main road leading north to Pristina.

On the way, they are searching for mines and booby traps left by the retreating Serb forces.

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

Ben Brown reports: "Nato can afford to take nothing for granted"

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

British and French troops are spearheading the initial thrust, with German, American and Italian forces due to move in later. The multi-national force for Kosovo will eventually number around 50,000.

Early in the day, British soldiers came across more than thirty Serb military and paramilitary troops, and disarmed them.

Advance upstaged

But the Nato advance was upstaged by the unannounced Russian advance into Pristina. The move came as Nato was still negotiating with Moscow about its role in the peacekeeping effort.

The Russian Foreign Minister Igor Ivanov immediately ordered them back out again. He said the troops did not have government authorisation to enter Kosovo.

But the BBC's Rob Parsons in Moscow says the Russian troops appear to have been acting on orders from the Defence Ministry, and they have shown no sign of withdrawing.

He says Russian generals are not happy with the agreement over Kosovo, and the events of the past 24 hours reflect that.

The column of Russian armoured cars, trucks and troop transporters was later reported to be parked on the road to the airport.

The BBC's Rageh Omaar: "They are not moving across the border yet"

A Russian solder said they had come to "prepare the airport for the arrival of Russian aircraft and then they would depart". He expected the unit would be there for two weeks.

Paras lead the way

British paratroops and Gurkhas on board Chinook helicopters were the first Nato soldiers to enter the province, at 0305 GMT.

Beneath them, thousands of troops began crossing the ground border at Blace - the same frontier post used by thousands of Kosovo Albanian refugees as they fled President Slobodan Milosevic's programme of ethnic cleansing.

Brigadier Adrian Freer, commander of the British 5th Airborne brigade and the first Nato officer to cross the land border at Blace, said: "We're going in to secure peace and make peace."

Although the international peacekeeping operation was launched with the authority of the United Nations, most of troops are from the Nato nations which carried out the air campaign against Yugoslavia.

French troops, led by mine clearing experts from the French Foreign Legion, moved into Kosovo along two lines of advance several kilometres apart and to the east of Blace.

Part of the advance was held up when special forces commandos detected a minefield just inside the province.

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

Vital road

The BBC's Paul Wood in Kosovo: "Jubilation among KLA fighters"

Paratroopers and Gurkhas are securing the landing zones and high ground above the road to Pristina.

Nato officials have planned for a "substantial" force to be in Kosovo by Saturday afternoon but have not released details of the operation.

In the hours before the troop movement, a British transport plane crashed on a military airfield near the Albanian town of Kukes, injuring one person.

Moscow talks

Moscow and Nato have been debating Russia's role since the peace deal was signed.

Talks between US Deputy Secretary of State Strobe Talbott, the Russian Foreign Minister, Igor Ivanov, and Defence Minister Igor Sergeyev lasted through the night until about 0600 local time (0200) on Saturday, and were then adjourned.

Correspondents say Mr Talbott had refused any modification to the UN-backed formula for peacekeeping in Kosovo.

• Flying into Kosovo
• Eyewitness: Inside Kosovo
• Kosovo Serbs pack up and leave
• Ground troops 'may have shortened war'
• K-For: The task ahead