The US military said Thursday it killed four Iranian-backed Shiite fighters and detained five others during operations north of Baghdad while Iraqi forces uncovered an explosives factory in southern Iraq, according to dpa. US troops came under attack during an operation in Rashidiyah, north of Baghdad, to detain a "special groups criminal" suspected of receiving money and weapons from Iran to launch attacks on coalition forces, the military said. "Special groups" is the US military term for bands of Shiite militiamen who have not observed a ceasefire declared by radical Shiite cleric Moqtada al-Sadr. The man and three other suspects were detained. Four other suspects were killed when US troops came under fire in another location, according to the military. In a separate incident, troops killed a suspected member of the al-Qaeda in Iraq group in Baghdad. The military said the man pulled a gun when his car was stopped by troops. Nine Shiite fighters were killed Tuesday by an Iraqi army patrol backed by US special forces in Husseiniyah, north of Baghdad, the US military said. The troops returned fire when the gunmen attacked their patrol using small arms weapons and rocket-propelled grenade launchers, according to the military. In the northern Salahaddin province, two US soldiers were killed and another soldier and an interpreter were injured in a road accident north of Baghdad, according to the US military. The two soldiers died when their vehicle rolled onto its side on Tuesday. The cause of the accident is under investigation. Iraqi security forces uncovered an explosives factory with up-to- date equipment in the southern city of Karbala, 110 kilometres south of Baghdad, the city police chief, General Raid Shakir, told the Voices of Iraq VOI news agency. Some 80 detonators, 23 bombs, 17 kilograms of TNT explosives as well as 8 kilograms of C-4 explosives were also found, the general said. In east Baghdad, a joint US-Iraqi force raided a mental hospital and detained staff and patients, a spokesman for the local health department told VOI. An Iraqi army force backed by multinational troops stormed Rashad mental hospital, smashed doors and detained everyone in the hospital, Qasim Abdel-Hadi said. The report could not be independently verified.