FACTBOX - Security developments in Iraq, March 25

(Reuters) - Following are security developments in Iraq at 1830 GMT on Tuesday.

* denotes new or updated item

BASRA - At least 12 people were killed in clashes in Iraq's southern oil hub of Basra on Tuesday, police said, after the Iraqi security forces launched a major operation against armed groups. Basra is 550 km (340 miles) southeast of Baghdad.

BAGHDAD - Fighting also erupted between followers of Shi'ite cleric Moqtada al-Sadr and supporters of a rival Shi'ite faction in and around Baghdad's Sadr City Shi'ite slum, police said. The U.S. military said clashes involving gunmen and Iraqi forces were under way in the area but did not give details of casualties.

* BAGHDAD - A mortar attack killed one U.S. soldier on patrol in the Adhamiya district of Baghdada, the U.S. military said. The mortar was fired from the vicinity of Sadr City.

* BAGHDAD - The Green Zone, the government and diplomatic compound, came under 12 indirect attacks that included 16 rockets, the U.S. military said. At least three people were wounded from the attacks, while structural damage in the compound was limited.

* BAGHDAD - U.S. military helicopters fired on armed gunmen in Sadr City to support coalition and Iraqi security forces protecting the area's checkpoints.

BASRA - Gunmen kidnapped three Iraqi policemen guarding a police training centre, police said.

BAGHDAD - Gunmen seized two police vehicles and kidnapped six policemen in the Maamil district of northeastern Baghdad, police said.