The US treatment of al Qaeda suspects at the X-Ray detention facility at Guantanamo Bay threatens to trigger the first rift between Britain and America since the start of the "war on terrorism".

Intervening in the growing row, Jack Straw has called for the prisoners to be treated "humanely and in accordance with customary international law".

"The British government's position is that prisoners - regardless of their technical status - should be treated humanely and in accordance with customary international law," Straw said in an official statement. "We have always made that clear and the Americans have said they share this view."

Tony Blair will today hear from UK officials who have visited the camp and talked to British nationals held there.

An announcement that the US plans to extend the controversial Guantanamo detention facility from 110 prisoners to 320 until a prison holding up to 2,000 is constructed is set to intensify human rights concerns.