A military judge on Thursday barred a Pentagon official from taking part in a second war crimes trial at Guantanamo Bay, providing more ammunition for lawyers of detainees who allege that political interference taints the proceedings.

A former chief prosecutor and defence lawyers have accused Air Force Brig Gen. Thomas Hartmann, the legal adviser to the tribunals, of demanding that certain cases be pursued over others based on political considerations.

Judge and Army Col. Steve Hanley ruled that Hartmann compromised his objectivity in public statements aligning himself with prosecutors and defending the Pentagon's system for prosecuting alleged terrorists.

Hartmann, who was also barred from the first Guantanamo war crimes trial, will not be allowed to provide further advice in the case against an Afghan detainee, Mohammed Jawad. But the judge rejected a defence request to dismiss war crimes charges against Jawad.

The former chief prosecutor, Air Force Col. Morris Davis, testified that Hartmann pushed for Jawad to be charged because the American public would be gripped by the details of the case — a grenade attack on two U.S. soldiers and their interpreter in Afghanistan.

"The guy who threw the grenade was always at the top of the list," Davis said.

The ruling "really affects some of the high-profile cases that Gen. Hartmann has had his hands in," said Jawad's attorney, Air Force Maj. David Frakt.

Khadr Case

Canadian Omar Khadr is due to stand trial for war crimes before a military commission in Guantanamo Bay in October.

The Hartmann ruling has already fuelled a defence challenge by Khadr's lawyers, who want the charges against the 21-year-old thrown out because of Hartmann's presence at the U.S. naval base, the Toronto Star reported Thursday.

If that doesn't happen, they want Hartmann expelled from future legal processes, said the Star.

Khadr is the only citizen of a Western nation still being held at the base in Guantanamo Bay. Khadr's lawyers filed suit on Aug. 8 in an effort to compel Prime Minister Stephen Harper to demand the Canadian citizen be repatriated.

Harper has said he won't get involved in the case because a legal process against Khadr is underway.

Legal influence

Hartmann supervises the chief prosecutor at Guantanamo and has extensive powers over the tribunal system. He testified Wednesday that he believed he was doing his job properly and said he has not offered to resign.

A judge in the trial of another prisoner, Salim Hamdan, disqualified Hartmann from participating in that case.

Hamdan was convicted last week and sentenced to 5 1/2 years in prison, concluding the first Guantanamo war crimes trial.