Russia, a traditionally ally of the Serbs, has been one of the strongest critics of the air strikes, accusing Nato of genocide.

But Moscow has so far ruled out any military role in the Kosovo crisis.

A Moscow woman denounces 'Nato killers'

Sources told Russian news agencies that the trip had been ordered by President Boris Yeltsin and that the premier would leave early on Tuesday.

The Russian Foreign Minister, Igor Ivanov, said on Monday that Moscow would take "additional steps" in a bid to halt the strikes.

He is expected to give details of a new settlement initiative at a press conference later on Monday.

Serb TV: 'Russian scum'

Mr Primakov's visit will follow a trip by a Russian peace mission to Belgrade which has come under fire from the Yugoslav state media. It has dismissed the three would-be mediators as Western stooges.

Former Russian Prime Minister Yegor Gaidar and former Deputy Prime Ministers Boris Nemtsov and Boris Fyodorov arrived in the Yugoslav capital on Sunday in an attempt to find a peaceful solution to the conflict between Belgrade and Nato.

The trio had earlier met US envoy Richard Holbrooke in Budapest who briefed them on Washington's stand on the Kosovo question.

A report on state-controlled Serbian television described the envoys as "scum and trash" who would "betray Serbian interests and their own country".

"While in Moscow and throughout Russia there is increasing bitterness and protests against the barbaric Nato aggression on Yugoslavia, envoys and the worst US mercenaries in Russia are coming to Yugoslavia," said the report.

'Belgrade ready to talk'

The envoys met Yugoslav Deputy Prime Minister Vuk Draskovic, who said Belgrade was ready to resume talks on Kosovo when Nato stopped bombing, the Russian agency Itar-Tass reported.

In the past Russia has often been called upon to use its influence in Belgrade to persuade President Slobodan Milosevic to seek a compromise. The two countries share the same orthodox faith and Slavic roots.