The US defence department has issued new instructions prohibiting physical or mental torture of prisoners.

The directive says all detainees shall be treated humanely and it specifically bans the use of dogs to intimidate those in custody.

The US has been criticised by human rights groups over its treatment of detainees from Afghanistan and Iraq.

Pentagon spokesman Brian Whitman said it was the first time such a directive had been issued.

Another directive, to be issued in the future, will define exactly what is meant by humane, he added.

On Monday, President George W Bush defended his government's treatment of detainees after a media allegation that the Central Intelligence Agency (CIA) ran secret jails in eastern Europe.

"We do not torture," he told reporters during a visit to Panama.