Syrian Anas Muhammad Khalid was sentenced to life in prison after being arrested in Falluja and being convicted of planning to lead attacks against security forces.
Another man captured in Falluja, Saudi-born Abd al-Majid Fayad al-Nizza was also given a life term on charges of crossing into Iraq from Syria to fight against the Iraqi government.
Syrian citizen Issam Anas Mahmud received a six-year jail sentence for entering Iraq illegally to join the armed fighters.
A Libyan, Fath Allah Abd al-Aati al-Rabati, also arrested in Falluja, was sentenced to 15 years in prison for entering Iraq illegally from Syria and having conducted "terrorist actions" against Iraqi security forces.
Egyptian Muhammad Hasan Abd al-Aal was sentenced to two years' imprisonment for having an expired entry visa after he was found with three other fighters in a house with weapons and ammunition.
The central criminal court, which convicted the men, was established under the US occupation to try major criminal and security cases. Many of the defendants who come before the court are held in US custody.
The International Committee of the Red Cross (ICRC) meanwhile on Monday confirmed that prisoners at a US-run detention camp in southern Iraq rioted on 1 April.
"There was a riot at Camp Bucca on 1 April. An ICRC delegation was there that day on one of its regular prisoner visits and it is now following up the situation," said Christophe Beney, the head of ICRC's Baghdad delegation.
Inside Camp Bucca where the US
has denied there is unrest
Earlier, a representative of Shia cleric Muqtada al-Sadr's movement had revealed that some detainees rioted at Camp Bucca on Friday after one of them had been denied medical treatment.
The al-Sadr representative accused US soldiers of putting down the disturbance with rubber bullets, wounding an unidentified number of detainees.
The US military, however, denies the rioting and mistreatment of prisoners.