Baghdad, Iraq ? Prisoners at Iraq’s largest detention facility protested the transfer of several detainees deemed “unruly” by authorities, throwing rocks and setting tents on fire in a disturbance that injured four guards and 12 detainees, the military said Monday.

Friday’s protest was the first of at least three violent incidents at Iraqi prisons during the past four days, with the latest occurring Monday at the notorious Abu Ghraib facility. A suicide bomber driving a tractor blew himself up outside the prison, wounding four civilians.

On Saturday, insurgents attacked Abu Ghraib with rocket-propelled grenades and two car bombs, wounding dozens of U.S. service members and prisoners, the U.S. military said.

Friday’s protest at Camp Bucca caused only minor injuries before being brought under control, authorities said.

Murtadha al-Hajaj, an official at radical Shiite cleric Muqtada al-Sadr’s office in the southern city of Umm Qasr, near Camp Bucca, said several al-Sadr supporters were wounded during the confrontation. He said they were protesting a lack of access to medical treatment and claimed U.S. guards opened fire, although he did not know if they wounded prisoners.

U.S. military spokesman Lt. Col. Guy Rudisill said he did not know if the guards opened fire, but he denied that any detainee was deprived of medical treatment.

Al-Qaida in Iraq said 10 of its fighters died in Saturday’s assault on Abu Ghraib, while the U.S. military put the insurgents’ casualties at one dead and about 50 wounded. Forty-four American soldiers and 13 prisoners were injured in the fighting — the latest in a series of large-scale attacks by insurgents in Iraq.