GUANTANAMO BAY NAVAL BASE, Cuba — The judge in the first American war crimes trial since World War II barred evidence on Monday that interrogators obtained from Osama bin Laden's driver, ruling he was subjected to "highly coercive" conditions in Afghanistan.

But Judge Keith Allred, a Navy captain, left the door open for the prosecution to use statements Salim Hamdan made at Guantanamo, despite defense claims that all his statements were tainted by alleged abuse including sleep deprivation and solitary confinement.

Hamdan, who was captured at a roadblock in Afghanistan in November 2001, pleaded not guilty at the start of a trial that will be closely watched as the first full test of the Pentagon's system for prosecuting alleged terrorists. He faces a maximum life sentence if convicted of conspiracy and aiding terrorism.

The chief prosecutor for the tribunals, Army Col. Lawrence Morris, said the loss of some of Hamdan's statements will not keep the trial from going forward.

"It does not reduce my confidence in our ability fully to depict Mr. Hamdan's criminality," he told reporters. "We're fine."

The judge said the prosecution cannot use a series of interrogations at the Bagram air base and Panshir, Afghanistan, because of the "highly coercive environments and conditions under which they were made."

At Bagram, the judge found Hamdan was kept in isolation 24 hours a day with his hands and feet restrained, and armed soldiers prompted him to talk by kneeing him in the back. His captors at Panshir repeatedly tied him up, put a bag over his head and knocked him to the ground.

Michael Berrigan, the deputy chief defense counsel, described the ruling as a major blow to the tribunal system that allows hearsay and evidence obtained through coercion.

"It's a very significant ruling because these prosecutions are built to make full advantage of statements obtained from detainees," he said.

A jury of six officers with one alternate was selected from a pool of 13 flown in from other U.S. bases over the weekend. Hamdan's lawyers succeeded in barring others, including one who had friends at the Pentagon at the time of the Sept. 11 attacks, and another who once taught a course taken by a person who is now a key government witness against Hamdan.

Monday marked the first time after years of pretrial hearings and legal challenges that any prisoner reached this stage of the tribunals.

The U.S. plans to prosecute about 80 Guantanamo prisoners, including the self-proclaimed mastermind of the Sept. 11 attacks and four alleged coconspirators.

Hamdan appeared to go along with the process despite earlier threats to boycott. The Yemeni with a fourth-grade education appeared to cooperate fully with his Pentagon-appointed military lawyer, whispering in his ear during the questioning of potential jurors.

"Mr. Hamdan expressed great interest in this," said Charles Swift, one of his civilian attorneys.

In addition to the other interrogations, the judge said he would throw out statements whenever a government witness is unavailable to vouch for the questioners' tactics. He also withheld a ruling on a key interrogation at Guantanamo in May 2003 until defense lawyers can review roughly 600 pages of confinement records provided by the government on Sunday night.

But Allred rejected allegations of a coercive culture at Guantanamo, where Hamdan testified that interrogators were gatekeepers for medical treatment.

The apparent link between medical care and Hamdan's cooperation with interrogators, he said, was "the natural consequence of agents seeking to help detainees in order to build rapport."

Hamdan has been held at Guantanamo since May 2002. A challenge filed by his lawyers resulted in a 2006 Supreme Court ruling striking down the original rules for the military tribunals. Congress and President Bush responded with new rules, the Military Commissions Act.

Hamdan met bin Laden in Afghanistan in 1996 and began working on his farm before winning a promotion as his driver.

Defense lawyers say he only kept the job for the US$200-a-month salary. But prosecutors allege he was a personal driver and bodyguard of the al-Qaida leader. They say he transported weapons for the Taliban and helped bin Laden escape U.S. retribution following the Sept. 11 attacks.