Live coverage l Map of overnight Nato strikes

Nato officials have rejected a Serbian declaration of a unilateral ceasefire in the province of Kosovo amid reports that it has carried out the heaviest night of bombing so far.

A BBC correspondent in Belgrade said explosions could be heard coming from the outskirts of the city on Tuesday night after the ceasefire was due to come into effect.

Kosovo is reported to have come under heavy fire with raids on an arms depot and the airport. Several strong detonations have also been heard in Montenegro.

The ceasefire came in an official statement from the Serbian and Yugoslav governments, which said "all actions against the aggressive Kosovo Liberation Army (KLA) will be unilaterally halted at 20:00 hours (18:00 GMT) in honour of the greatest Orthodox Christian holiday, Easter".

Reaction to Belgrade's offer was swift.

The UK Prime Minister Tony Blair called the truce plan "a diplomatic ploy" the West would "not fall for".

Nato's Secretary-General Javier Solana rejected the proposals as "insufficient."

Brian Hanrahan reports: "A ploy to consolidate their position"

"Before a ceasefire can be considered, President Milosevic must meet the demands established by the international community," said Mr Solana.

Nato member states are demanding that a ceasefire be accompanied by a withdrawal of Yugoslav forces from Kosovo, a return of refugees and a halt to the repression of ethnic Albanians in the province.

BBC World Affairs Editor John Simpson: "This may just be an excuse to stop"

"We've made very clear that any hollow, half measures will not stop the bombing," said David Leavy, spokesman for the White House National Security Council, within minutes of the announcement.

US Defence Secretary William Cohen said the Serb ceasefire idea was "not only completely unacceptable but absurd".

But Russia's President Boris Yeltsin said that he welcomed the initiative in principle.

Yugoslav compliance

Shortly after the ceasefire came into force, Serbian TV reported that all Yugoslav army units in Kosovo were complying with the order from Belgrade.

Yugoslavian Deputy Prime Minister Vuk Draskovic: "We will discuss withdrawing troops once bombing raids on us have stopped"

The Yugoslav Ambassador in New York, Vadislav Jovanovic, said that the rejection of the offer is a "public admission that Nato countries are more interested in continuation of the war than in seeking peace".

"Their insistence on such a position is evidence that arrogance takes precedence over common sense," said Mr Jovanovic.

Flames and smoke rise in Kosovo near the Albanian border on Tuesday

The Yugoslav statement pledged future discussions with the moderate ethnic Albanian leader, Ibrahim Rugova, on a final settlement to the crisis.

It also promised that Belgrade would work for the return of about 400,000 ethnic Albanians who have fled Kosovo.

Heaviest bombing yet

Nato says clearer skies on Monday night allowed its forces to carry out the most intensive air attacks over Yugoslavia so far, and reports say bombing will intensify yet further.

William Horsley: "Apache helicopters will soon be arriving to step up the attacks"

Bridges, air defence radars and communications, airfields, police headquarters and petroleum facilities were targeted by missiles and bombs.

Serbian media reported a strike on the southern mining town of Aleksinac had killed at least five people and injured another 30. Yugoslav officials said later that the figure had increased to at least 12 dead.

Television reports said about 10 buildings had been destroyed, as well as a centre for emergencies and a medical dispensary.

David Shukman reports: "The Serbs have become elusive"

At a Nato briefing in Brussels, Air Commodore David Wilby said a missile which struck the town of Aleksinac had been 600 metres short of the military post targeted and may have hit a residential area..

Air Commodore Wilby said an investigation was under way to establish what had happened.

Airlift under way

Some of those displaced by the turmoil in Kosovo have begun to be airlifted out of refugee camps to other countries which have promised to accept them on a temporary basis.

The first of those refugees were reported to be arriving in Turkey, which has promised shelter for 20,000 people escaping Serbian violence.