Air Commodore David Wilby said Nato's new strategy of targeting infrastructure is already hitting supply routes to Serb forces in Kosovo.

He said: "Serb police are paying a heavy price for their campaign of terror, their crimes against humanity.

"But they are continuing to terrorise the Kosovo Albanian population. The result of their brutal activity is a single large triangular area that has been ethnically cleansed."

Air Commodore Wilby said a number of targets, including strategically important infrastructure, had been attacked during air strikes on Thursday night.

He said Serb troops were experiencing greater difficulty getting vital supplies, and that one battle group was immobolised while it waited for fuel.

'Ghost towns'

Nato spokesman Jamie Shea told the daily media briefing at the alliance's headquarters on Friday, that one-third of the pre-conflict Kosovo population had been displaced.

He said: "There is a clear strategy of creating a series of ghost towns. The latest is Pristina, the regional capital, where 30,000 people have been rounded up and forced to leave.

"We are no longer facing an internal Yugoslav crisis. It is a crisis of the entire region."

Mr Shea also said there was concern at the fate of Kosovo Albanian men aged between 16 and 60.

He said: "We have reports of them being herded into camps, and used as human shields."