These people are accused of having been members of the most dangerous terrorist organisation that the world has ever seen

Foreign Secretary Jack Straw

There have been allegations that detainees were shackled, drugged and hooded as they were flown to Cuba, although the US says they are being treated "very humanely."

The American military has promised that British representatives will be allowed to visit the men, but have yet to agree on how and when the access will be granted.

A spokeswoman for the British embassy in Washington said discussions were under way on the issue.

"This is obviously an unusual situation," she said. "What is happening at the moment is that there is very close collaboration and discussions between us and the US."

Speaking earlier on BBC Radio 4's Today programme, Mr Straw said the government was seeking reports into the conditions in which the men were being held.

But he said it must not be forgotten the men were accused of being members of the most dangerous terrorist organisation in the world.

He added it would be some time before he would be able to give final confirmation that the three men were British.

'Responsibility'

Meanwhile four Labour backbenchers have called on the UK Government to push the US to treat the men as prisoners of war and observe Geneva Convention.

Mr Straw told Today the men would be visited by British consular officials, and said the International Red Cross was also going to Cuba to check on the conditions in which the prisoners were being held.

Pressure is mounting for captives to be treated as prisoners of war

Six more Britons suspected of links to the Taleban or al-Qaeda in Afghanistan are reportedly being sent to the camp.

He had spoken to US Secretary of State Colin Powell on Saturday to discuss the issue.

He said the men were assumed to be al-Qaeda members but that did not mean that the men did not have rights.

"It is our responsibility to see that they receive those rights," he said.

The foreign secretary said he would not condemn the conditions in which the men were being held unless there was cause for concern once reports on conditions had been received.

Geneva Convention

With regards the men being shackled and possibly hooded on the plane, he said he had not protested because of the "special circumstances" of the accusations against them.

"I defy anybody to say how you could transport potentially profoundly dangerous prisoners other than by wholly restraining them and ensuring that they couldn't signal with each other.

"Whether or not technically they have rights under the Geneva Convention, they have rights in customary international law."

Earlier the prime minister's spokesman said the US had given assurances the prisoners were being treated in accordance with "international norms of behaviour".

Razor-wire pens

US assistant secretary of defence for public affairs Victoria Clarke told reporters that "all security precautions were being taken" but the detainees were receiving "culturally appropriate" meals and had access to showers and medical treatment.

She said the International Committee of the Red Cross would be given access to the detention facility "later this week".

The captured men are said to be kept separate in make-shift cells, made from chain link fencing, measuring 1.8 by 2.4 metres (six feet by eight feet).

The cells have mattresses, concrete floors and wooden roofs, and are inside razor-wire pens.

In all, 2,000 men are expected to be transported to the base, which is leased by Cuba to the US military.

The US described the first 20 detainees as the "worst elements" of the al-Qaeda terror network.