Improved weather conditions allowed for intensive attacks across Yugoslavia on Monday night.

British forces have kept up the pressure with RAF Harrier GR7s launching their first successful daylight raids against Sebian ground forces in Kosovo.

Group Captain Ian Travers Smith, speaking at the Italian air base at Gioia del Colle, said cluster bombs were used for the first time to target mobile army and paramilitary units.

George Robertson: Attacks will continue

Pilots returning to the base were "confident" they had taken out the targets, believed to include tanks, he added.

Two previous daytime search and destroy missions against Serb troops had failed.

"We suspect that the Serbs realised the advantage that the better weather gives us, and are going to great lengths to hide their heavy equipment to escape detection," said Vice Admiral Sir Ian Garnett, chief of joint operations.

Grp Capt Travers Smith said: "It seems from what has gone on today that he (Mr Milosevic) has not hidden them quite well enough."

Casualty reports

As Nato's military campaign is stepped up, there have been Serb reports of civilian casualties.

Speaking at a Ministry of Defence briefing in London, Defence Secretary George Robertson said that if the reports were true, they would be "deeply regrettable".

But Mr Robertson said they must be set against "the tide of misery which Milosevic has inflicted on the people of Kosovo".

Reported Serb casualties "deeply regrettable"

"We are systematically cutting the sinews of Milosevic's war machine.

"Air operations will continue without let up for as long as may be necessary to secure our aims," he said.

'Vile ethnic war'

The defence secretary said Nato was hitting key parts of the Yugoslav military structure - highways, bridges, command and control centres, steel and ammunition dumps, air defence sites, tanks, artillery and barracks.

"We shall continue with our attacks as long as is necessary to ensure Milosevic is defeated in his vile ethnic war. Milosevic should be absolutely clear: we are not going to go away," he said.

He insisted Nato's actions were a "proportionate response to Milosevic's intransigence. It is not indiscriminate. It is carefully targeted".

He said that, in contrast, Serbs were systematically targeting the general civilian population.

Mr Robertson said more than 500,000 people had been "driven into exile and suffering by Milosevic's brutal ethnic campaign. Many of those are at risk and some of them will almost certainly die. It is that wider tragedy which Nato is working to stop."

He said the Serb leadership continued to deny it was carrying out "ethnic cleansing", claiming it was a victim of aggression by Nato.

'Blatant' propaganda

The defence secretary described this as "blatant propaganda" and said the people of Serbia were being kept ignorant of what was being done in their name.

Refugees continue to pour out of Kosovo

He said: "Their ignorance is a direct result of the iron grip which Milosevic has on the media in Serbia.

"But we will expose the truth of this terrible war. Milosevic will be unmasked. Our purpose is to defeat Milosevic's campaign of ethnic warfare."

Mr Robertson also revealed that HMS Splendid, the Royal Navy's Tomahawk cruise missile submarine, had been reloaded with missiles and will be ready to carry out further attacks within the next 24 hours.

Refugee crisis 'extremely serious'

During the briefing, International Development Secretary Clare Short warned that huge numbers of people could die because of delays in allowing refugees from entering Macedonia.

Ms Short, who has just returned from Macedonia, said she witnessed the confusion on the border at Blace and said the situation was "extremely serious".

Refugees at the Blace camp want to go home

She said the Macedonian government's ban on allowing more than 50,000 refugees from entering the country was damaging its image and would harm its relations with the West.

"There is no reason for any delay and we must ensure no more obstacles are put in their way. Otherwise there will be an outbreak of disease and a real risk that large numbers will die," she said.

The refugees she had spoken to had thanked her for the Nato campaign and said they wanted to return home to Kosovo.

She also said Britain was taking a lead in speeding up provision for the care of refugees. Eleven flights have been set aside to bring food and essential supplies to Albania and Macedonia.