Speaking after warning Nato not to send ground troops to the region, Mr Yeltsin said: "I told Nato, the Americans, the Germans, don't push us towards military action.

"Otherwise there will be a European war for sure - and possibly world war," he added in televised comments.

As the war of words escalated, reports from Albania said some 2,000 refugees had crossed over from Kosovo - reportedly after being forced to leave by Serb forces.

It was the first major movement of Albanians from Kosovo since Yugoslavia announced the border was closed three days ago.

Meeting to defuse tension

President Yeltsin said Russia could not allow Nato to ''seize'' Yugoslavia and turn Kosovo into a protectorate.

Moscow has previously said it would not consider military involvement in the Balkans in any circumstances.

The US Secretary of State Madeleine Albright and Russian Foreign Minister Igor Ivanov will meet in Oslo on 13 April to discuss the crisis.

Nato's supreme commander, US General Wesley Clark, said the alliance would not halt its bombing campaign against Yugoslavia in response to Russia's warnings.

"We're going to continue with the mission exactly as planned regardless of political and diplomatic atmospherics," he added.

The BBC's Brian Hanrahan: The prospect of Russian military involvement has set alarm bells ringing

The United States says it is sending six more F-15E fighter jets to Europe for use in the Nato campaign and is leaving a ship with a hospital on it in the Mediterranean to help with refugees.

BBC Moscow Correspondent Andrew Harding says Mr Yeltsin's comments were probably designed more to appease domestic critics than to alarm Nato.

Mike Hammer of the National Security Council: We have received assurances at the highest level from Russia

Washington says it has been assured at a high level that Russia will not get involved in the conflict.

Nato spokesman Jamie Shea said earlier reports that Russian missiles would be retargeted at western alliance nations should be taken ''with a pinch of salt".

Parliamentary speaker Gennady Seleznyov had been reported saying the Kremlin had ordered missiles to be pointed at countries targeting Yugoslavia. But a spokesman said the remarks had been misunderstood.

Car factory hit

Nato's latest bombing raids were hampered by poor weather.

(Click here for a map showing Nato's latest strikes).

Thousands of Serbs also formed human shields to protect key bridges from attack.

Amid the bombing, Serbs celebrate Easter

The alliance hit a car factory in Kragujevac, which it says was also manufacturing arms. Serb TV reported 120 people were injured and said bombs also struck a plant providing heating to homes, hospitals and schools in the town.

Nato said there might have been "collateral damage" to civilian buildings near the factory, but had no figures for casualties.

The alliance also admitted that a bomb aimed at a telephone exchange in Pristina earlier this week struck a residential district after falling short.

The BBC's David Shukman reports on Nato strategy: "Other scenarios are opening up"

Other overnight targets included a power line in Valjevo, a fuel depot in Smederevo and a television transmitter, believed to be used for military communications.

On the ground in Kosovo, there have been reports of fighting between Serbian troops and Kosovo Liberation Army forces near the Albanian border.

Gunfire was exchanged on Friday and two mortar shells landed in Albanian territory, a spokesman for the Organisation for Security and Co-operation in Europe said.

Refugee mission

The United Nations Secretary General, Kofi Annan, urged the Yugoslav authorities to cease all military action in Kosovo so that ''the tragedy'' there could be brought to an end.

He also appealed to Belgrade to end its expulsion of Kosovo's civilian population immediately, and allow the unconditional return of all refugees.

He said Belgrade must accept the deployment of an international military force to ensure the refugees' safe return.

In Macedonia, the UN High Commissioner for Refugees, Sadako Ogata, has toured one of the largest tent camps for Kosovo Albanians.

The Macedonian foreign minister, Aleksander Dimitrov, says Nato has given his country new assurances for security if Serb forces attacked or if the conflict spilled over the border.

But the minister, speaking after talks at Nato's headquarters in Brussels, said Macedonian territory could not be used for offensive action against any neighbouring country.

In Yugoslavia, a mission by the speaker of the Cyprus parliament, Spyros Kyprianou, to secure the release of three captured American soldiers has ended in failure.

• Mission to free soldiers fails
• Uranium weapon fears in Kosovo
• Russian public demands action
• Milosevic is feeling the heat
• Refugees 'lost' in Kosovo

The UNHCR says the number of people who have fled Kosovo since 24 March, when Nato began bombing Yugoslavia, is now more than 620,000.