The former cook of al-Qaeda's Osama bin Laden has had his Guantanamo prison sentence reduced to two years from 14, under a plea agreement that remains secret.

The US military said Ibrahim al-Qosi's sentence had been reduced on Wednesday, contingent on his adherence to agreed upon terms.

Those terms included an agreement not to engage in or materially support hostilities against the United States or its coalition partners.

Al-Qosi, who is about 50, acknowledged in his plea agreement that he knew al-Qaeda was a terrorist group when he ran one of the kitchens in bin Laden's Star of Jihad compound in Afghanistan.

A Sudanese, he was one of the first terrorism suspects taken to Guantanamo in 2002, and pleaded guilty in July last year to to charges of conspiring with al-Qaeda while being under pressure and providing material support for bin Laden and the group.

He has admitted helping the al-Qaeda leader escape US forces in the Tora Bora mountains of Afghanistan after the US invasion in 2001.

But he said he had no involvement in or prior knowledge of any terrorist acts, including the September 11, 2001 attacks on the United States, which prompted the US invasion.

Al-Qosi is one of 172 captives held at the Guantanamo prison in Cuba, and one of only three held there who have been convicted of crimes in the controversial military tribunals. Two other men convicted in the tribunals served short sentences and were sent home to Australia and Yemen.

Al-Qosi's lawyers said last year that once he returned to Sudan, he would enter a programme run by the Sudanese intelligence service and designed to rehabilitate those with "radical views". He would then return to live with his family but would be monitored to ensure he had no contact with radicals, they said.