Despite firm opposition from the White House, the US Senate has explicitly barred US soldiers from torturing or mistreating prisoners in a measure outlining strict military interrogation guidelines that passed late last night by 90 votes to nine.

The measure - an amendment to a $440 billion defence spending Bill being debated in Congress this week - aims to prevent "cruel, inhuman, or degrading treatment or punishment of persons under custody or control of the United States Government".

Senator John McCain, who along with fellow Republican Lindsey Graham drafted the measure, had predicted that it would pass easily.

"The effect would be that the men and women who are doing the interrogations would feel comfortable in knowing that they have exact instructions as to what they can and cannot do," said Mr McCain, a decorated war veteran who spent more than five years in a Vietnam prison camp.

"It would send a message throughout the world where America’s image is suffering that we will not condone any practice that is cruel or inhumane."

The amendment is a response to the damaging 2004 prison abuse scandal that erupted following the publication of pictures that showed US military personnel humiliating and abusing inmates at Abu Ghraib prison near Baghdad.

The photos showed detainees piled up naked on the floor in front of US soldiers, cowering in front of snarling military dogs, chained to beds in stress positions and forced to stand naked in front of female guards.

The measure states that "no person in the custody or under the effective control of the Department of Defence or under detention in a Department of Defence facility shall be subject to any treatment or technique of interrogation not authorised by and listed in the United States Army Field manual on intelligence interrogation".

"The image of the United States was very badly harmed by the pictures of prisoner abuse," said Mr McCain."We have to send a message to the world that we will not ever allow such kind of treatment to be repeated."

President Bush, however, has vowed to veto the measure. "There still seems to be significant opposition from the White House and the Department of Defence," Mr McCain said. "We’ll have to keep working it."

But he added that members of the US military have contacted him expressing support for the measure. "We’re hearing from men and women in the military all the time. They don’t like to see their image tarnished by allegations of misbehaviour such as Abu Ghraib and other instances."

From the floor of the Senate, Mr McCain also read a letter of support from Colin Powell, the former Secretary of State who once served as the chairman of the Joints Chiefs of Staff.

"I fully support this amendment," Mr McCain said, reading from the letter. "The world will note that America is making a clear statement with respect to the expected future behaviour of our soldiers. Such a reaction will help deal with the terrible public diplomacy crisis created by Abu Ghraib."

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