Osama bin Laden's former chauffeur has been found guilty of supporting terrorism, in the first verdict to be delivered by the US's war crimes tribunal at Guantanamo Bay.

But the jury of six American military officers found Salim Hamdan not guilty on a second and arguably more serious charge of conspiracy, after three days of deliberations. He now faces a potential life sentence.

The outcome is likely to be hailed as a qualified success for the Bush administration, vindicating its dogged determination to press ahead with the controversial system of military tribunals for Guantanamo detainees, despite the many legal objections over the last seven years.

In a sign of how closely it was watching proceedings, a White House spokesman said in a statement within minutes of the verdicts that the Bush administration was pleased that Hamdan received a fair trial.

The split verdict follows a two-week military trial at the US naval base on Cuba – the first war crimes trial in the US since the Second World War.

Hamdan, a Yemeni estimated to be aged about 40, was arrested at a roadblock in Afghanistan in November 2001, soon after the US invasion which deposed the Taleban regime that was harbouring Mr bin Laden and his al-Qaeda associates.

He was found to have two surface to air missiles in the car.

During the trial John Murphy, the Justice Department prosecutor, described Hamdan as among the worst of Mr bin Laden’s henchmen.

"He’s an al-Qaeda warrior. He has wounded, and the people he has worked with have wounded the world," Mr Murphy told the jury.

His defence lawyers, however, depicted him as a minor figure with no involvement in plots, who had been found guilty by association. They said he was a paid employee of Mr bin Laden from 1997 to 2001 who earned $200 a month, but was not a member of al-Qaeda and took part in no attacks.

"We will capture or kill Osama bin Laden some day. You should not punish the general’s driver today with the crimes of the general," said Navy Lieutenant Commander Brian Mizer, the Yemeni man’s court-appointed military attorney. He added that not a single witness had testified to Hamdan taking part in terror attacks.

Hamdan, wearing a white turban and long white robe topped with a tan blazer, stood tensely in the courtroom beside his lawyers as the verdict was announced, listening through headphones to the English-Arabic interpreter.

The defence team has already indicated that it will appeal against a guilty verdict.

Since his arrest, Hamdan has spent six years in the US prison camp at Guantanamo.

His trial is widely seen as a test of the controversial military commission system set up by the Bush administration, which had already suffered a chequered history before delivering its first verdicts today.

The military commissions were invalidated in 2006 by the Supreme Court, only to be restored a few months later by the US Congress. They have since been struck by further legal battles and hitches that pushed back the opening of Hamdan’s lawsuit and those to follow. About 270 suspects remain in detention in Guantanamo Bay.

Prosecutors say that the system offers suspects a fair trial, but human rights advocates and defence lawyers say that it is fundamentally unfair, allowing confessions obtained through alleged torture to be used as evidence, that would not be admissible in any other courtroom.

The Bush administration argues that accused terrorists cannot be tried in the ordinary way as if they were soldiers in uniform. It has reserved the right to detain indefinitely those it designates as unlawful enemy combatants.

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