The warning came as Nato intensified its air campaign, carrying out 684 sorties over Yugoslavia on Friday, the highest number so far in a single day.

In his first full briefing since the conflict started, Lieutenant-General John Reith said it could take two years to repair the devastation inflicted by Serb forces.

Lieutenant-General John Reith: "They gutted most of the homes"

He said: "When the Serbs evicted the people from Kosovo they did tremendous damage, particularly to the outlying villages.

"That will take time to repair, and my experience from Bosnia was that even two years later, many of the houses had not been repaired," he added.

The flood of refugees out of Kosovo has meanwhile been continuing unabated.

BBC Diplomatic Correspondent Kevin Connolly: "A huge task ahead"

Thousands more people crossed into Albania late on Friday. Most were from the village of Suvareka, near the southern town of Prizren.

Some told the BBC they had been hiding out in forests for over two months since being expelled from their homes.

Armoured vehicles hit

The BBC's Nick Childs at Nato headquarters: "The highest number of sorties since the air campaign began "

Taking advantage of good weather, Nato planes carried out an unprecedented number of sorties, hitting a wide range of targets.

The attacks were directed against the Serbian electricity transmission system, as well as ammunition storage facilities, bridges, army barracks, television and radio transmitters.

Nato says that at least 12 tanks were hit in Kosovo, as well as 11 other armoured vehicles and nine artillery positions.

Most of Serbia's largest cities were reported to be without electricity on Saturday morning after Nato planes dropped graphite bombs on a number of power plants overnight.

Serb media said 10 workers at one plant to the southwest of the Yugoslav capital Belgrade were injured in the raids.

The capital was also said to have been targeted during the night. Unconfirmed reports speak of a number of powerful explosions at fuel depots in and around the city.

(Click here to see a map of the latest strikes)

Ground troops

The BBC's Clive Myrie: "Those we spoke to said they had been through a terrible ordeal"

With no breakthrough in sight on the diplomatic or military fronts, Nato is facing pressure to make a decision on sending ground troops into Kosovo.

Nato commander Gen Wesley Clark reportedly told US military chiefs there was no guarantee the air campaign against Yugoslavia would succeed before winter sets in, and a decision on "other options" was needed soon.

Ken Bacon: Plans to beef up Nato's peacekeeping force

Pentagon spokesman Ken Bacon said Nato would probably discuss a plan next week for a force of up to 50,000 troops to join Nato's KFOR peacekeeping force - up from a previously-agreed figure of 28,000.

Mr Bacon said: "We're going to need a larger KFOR, and we want it deployed in Macedonia as quickly as possible, because, should there be a peace agreement quickly ... we need a force that's ready to go in ... as the Serb forces pull out"

Serbs 'diminished'

The UK Foreign Minister Robin Cook, who met US Secretary of State Madeleine Albright on Friday, said the time was nearing when Serb troops in Kosovo would become so diminished by allied bombing that they could not mount an organised defence against a NATO ground force.

He said: "I don't see any sign that the Yugoslav army at the present rate of attrition is going to hold out until August or September."

The first Nato F-18 attack aircraft were due to arrive in Hungary on Saturday.

While Hungarian air space and airports have been used since the beginning of the operation, these will be the first planes to take off from Hungarian soil to attack targets in Yugoslavia.

• Analysis: The shifting diplomatic scene
• Nato: Prison bombing 'justified'
• Analysis: The war for hearts and minds
• Anti-Yugoslav protest in Montenegro
• Children's tales of horror

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