A 39-year-old Yemeni accused of being an aide to Al-Qaeda leader Osama bin Laden was sentenced to life in prison Monday by a military tribunal at Guantanamo Bay, Cuba, a Pentagon spokesman said.

Ali Hamza Ahmad al-Bahlul, an alleged aide and media secretary to Bin Laden, was convicted Friday by a military panel of charges of conspiracy, solicitation to murder and terrorist acts, and providing material support for terrorism, said Commander Jeffrey Gordon.

It was the second trial of a `war on terror` detainee at Guantanamo Bay under a specially created system of military commissions that has been criticized by civil rights activists and lawyers as lacking full protection of defendants` rights.

Bahlul boycotted the trial and, on his instructions, his court-appointed military lawyer remained silent throughout the proceedings, said Jamil Dakwar, who observed the trial for the American Civil Liberties Union.

`Unfortunately, because the system is fundamentally flawed and lacks any semblance of due process, a cloud of illegitimacy hangs over this verdict,` Dakwar said.

`The next president should close Guantanamo and future prosecutions should occur in criminal or military courts where the constitution still means something and where verdicts, no matter what they are, can be trusted,` he said.

The nine-member military panel deliberated for less than four hours before reaching a verdict, he said.

The sentence was the stiffest yet.

In the first such trial, Osama bin Laden`s former driver Salim Hamdan was sentenced in August to a net of five months in prison, after the considering the years he had already spent in US detention.

Military jurors found Hamdan guilty of providing material support for terrorism, but rejected stronger terrorist conspiracy charges.

Australian David Hicks pleaded guilty to a charge of material support for terrorism in March 2007 under a plea deal in which he was allowed to serve out most of his nine-month sentence in Australia.

The Pentagon said Bahlul`s case will undergo automatic review by the Pentagon official overseeing the trials, and then by a Court of Military Commission Review.

He can then appeal the verdict to the US Court of Appeals and the Supreme Court.

The US military alleged that Bahlul was Al-Qaeda leader Osama bin Laden`s personal secretary and his media secretary.

It charged he underwent military training at an Al-Qaeda camp in Afghanistan, swore allegiance to bin Laden and helped produce numerous propaganda videos.

They allegedly included a video entitled `The destruction of the American destroyer USS Cole,` depicting the October 12, 2000 bombing attack on the US naval ship in Yemen, which killed 17 American sailors.

According to the charges, the video aimed `to solicit material support for Al-Qaeda, to recruit and indoctrinate personnel to the organization and objectives of Al-Qaeda and to solicit, incite and advise persons to commit terrorism.`

Bahlul is also accused of preparing the video of the last `martyr wills` of Mohammed Atta, the leader of the 19-man team that hijacked four passenger jets to crash them into US buildings on September 11, 2001.