But, as on Thursday night, poor weather prevented many planes from attacking their intended targets.

Nato spokesman Jamie Shea said only one in four combat groups of planes had been able to complete its mission.

(Click here for a map showing latest strikes)

Assurances over Russia

Nato leaders are putting a brave face on persistent setbacks in the air campaign caused by problems of visibility.

General Wesley Clarke, the commander of allied forces in Europe, said the missions would go on "regardless of political and diplomatic atmospherics", a reference to the sharp warning to Nato from Russia's President Yeltsin not to push Russia into a European war.

The UK Foreign Secretary Robin Cook has given reassurances that Russia had no intention of getting involved in the Kosovo conflict in a 45-minute telephone conversation with his Russian counterpart Igor Ivanov.

Foreign Office Minister Doug Henderson told a news conference the two men had a constructive discussion.

"They both agreed that they should maintain close contact to try to avoid any increase in tension and to maintain the strong relationship between the two countries," he said.

Serb military 'weakened'

Mr Henderson went on to reject suggestions that air strikes were ineffective.

"We have weakened and disrupted President Milosevic's military machine. We have seriously damaged his ability and that of his forces to sustain a campaign of terror and repression. We have damaged airfields, destroyed air defences and aircraft," he said.

The head of operations, Air Marshal Sir John Day, confirmed that cloud cover had led to the cancellation of most bombing missions.

But he said cruise missile attacks involving the submarine HMS Splendid had continued.

'Temporary respite'

Attacks had focused particularly on the Serbs' remaining fuel supplies. Mr Henderson said that once the weather cleared the Nato assault would resume with renewed intensity.

Igor Ivanov: Reassuring talks

"The weather can give a breathing space for a night or two but the soldiers on the ground know that the next attack is only a matter of time and they have no protection from such attacks," he said.

"Mr Milosevic will know this is a temporary respite. When the weather clears the bombardment will resume with increasing ferocity."

Nato is under great pressure to show better military results.

Even the Apache attack helicopters being sent to drive back Serb forces in Kosovo, cannot be used at once because Serb air defences still pose too great a risk.

Asked to say how long the air campaign would have to go on, a Nato spokesman said he hoped it would be over in days but it would have to continue for as long as it takes.