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Speaking at the beginning of a two-day visit to the region, Mr Cohen said a number of heavy bombers and other warplanes would be sent home from the UK's Indian Ocean island of Diego Garcia.

This follows news that the US has declared it is prepared to allow Iraq to sell more oil, so it can buy more food and medicine.

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Mr Cohen said although troops would be cut back by around a quarter, some 20,000 would remain in the area to renew attacks on Iraq if President Saddam Hussein threatened American allies.

"We have the ability to react very quickly so we're satisfied that our day-to-day force is adequate," he said.

UN workers return to Iraq

As about 100 United Nations relief staff resumed work in Iraq, overseeing the distribution of humanitarian supplies under the oil-for-food programme, the Iraqi authorities banned a UN plane from landing near Baghdad - forcing UN special envoy Prakash Shah to leave the country by road.

An unnamed UN official said: "The Iraqis told us that all UN flights are banned until further notice."

Before the air strikes, UN planes flew regularly into Habania airport and were used extensively by UN weapons inspectors as well as Mr Shah, the special representative of Secretary-General Kofi Annan in Baghdad.

'Tool to justify military action'

Meanwhile, one former Unscom inspector has accused Britain and the US of using out of date information to justify the air strikes on Iraq, while weapons inspections centred on sites intended to provoke the Iraqis.

Scott Ritter, the former head of the UN weapons inspection team in Iraq, said data on which inspections were based was often "months, maybe years old".

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Sites for inspection were often chosen not for disarmament reasons, but to provoke the Iraqis, he told Radio 4's Today programme.

Mr Ritter blamed the US for that provocation, and said Unscom chief weapons inspector Richard Butler was also guilty for complying with American pressure.

Mr Butler had "allowed the United States to manipulate the work of Unscom in such a fashion as to justify an air strike".

The problem was not deadlines for inspection, but manipulation of the process so it became a "tool to justify military action", Mr Ritter said.

Scott Ritter: Unscom inspection was rushed through to provoke an Iraqi response

And Mr Ritter told BBC News Online that the US and British action against Iraq had only made matters worse.

"Nothing was gained from these strikes, and much was lost, to include Unscom itself," he said.