The official media in Yugoslavia said Nato air strikes on Monday night had caused civilian casualties and damage, despite Nato's insistence that it was attacking only military targets.

State television and the official Yugoslav news agency Tanjug said at least one person was killed during a 20-minute air raid on the southern city of Nis and a satellite station in southern Serbia was damaged.

The reports said houses, a tobacco factory and a building supplies plant were wrecked. Elsewhere, a series of explosions was reported in Kosovo's main city of Pristina and near the Yugoslav capital, Belgrade. There were no details of damage or casualties.

Reinforcements expected

Paul Reynolds: Task Force Hawk begins to deploy

The bombing reports came as the US announced an extra 500 paratroopers on their way to Albania.

US officals said the fresh forces would support Nato's Task Force Hawk, a new mission involving 24 Apache ground-attack helicopters, expected in Albania on Tuesday.

The craft, which will be used to hit tanks and other military vehicles inside Kosovo, have been delayed by bad weather.

The UK Prime Minister, Tony Blair, is in Brussels to discuss the progress of Operation Allied Force with Nato leaders before meeting British forces on active service.

The UK has also announced that it will do all it can to bring what it called the perpetrators of the atrocities in Kosovo to justice.

Foreign Secretary Robin Cook said he was authorising the largest-ever release of intelligence material to help war crimes investigations.

Massive movement

The BBC's Dumeetha Luthra: Speculation that Nato is preparing for ground troops in Kosovo

The World Food Programme has said an estimated 800,000 people are heading for the Albanian, Montenegrin and Macedonian borders.

Aid workers on Kosovo's borders said they were expecting another huge wave of refugees to arrive at any time, although the numbers of those now crossing have been reduced to a trickle.

A UN spokesman said that Serbian forces were forcibly preventing people from leaving Kosovo.

Mike Williams: Targets appear to be industrial zones of Nis

Serbian reports said that 20,000 refugees had returned voluntarily to their villages near Podujevo in northern Kosovo, after being forced out by Nato bombings and separatist attacks.

The government in Montenegro - which together with Serbia makes up the Yugoslav federation - has said it is investigating reports that Yugoslav forces have expelled local ethnic Albanians from their villages close to the border with Kosovo.

US-Russian talks

Diplomatic efforts are going on alongside the military build up.

Nato is building up its base in Albania

The US and Russian presidents spoke by phone for 50 minutes on Monday night - their first direct discussion on Kosovo since the Nato strikes started.

They failed to reconcile their differences over the handling of the crisis, but agreed that Russia would not become involved in the conflict militarily.

Russian reports said President Boris Yeltsin again demanded a halt to the bombing, and criticised Nato's demand that it led a Kosovo peacekeeping force to supervise the return of refugees.

The head of the Russian Orthodox Church, Patriarch Alexiy, is due in Belgrade on a separate peace mission.

Media fears

As Nato's bombing of Yugoslavia continued on Monday, Western journalists were invited by the Serbian information minister to visit the headquarters of Serb TV station RTS in the centre of Belgrade.

The move followed rumours that it might be targeted by Nato. One American television channel, which had a satellite facility there, pulled out all its equipment and many of the other Western organisations cancelled their satellite transmissions.

BBC World Affairs Editor John Simpson - who is in Belgrade - said several organisations, including the BBC, had decided not to take part in what would presumably have been a propaganda exercise.

Nato on Monday admitted its warplanes may have caused civilian casualties in attacks on two convoys in Kosovo last week.

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