Basra, some 550 km south of Baghdad, has been the scene of a fierce clashes between the Iraqi security forces and Mahdi Army militiamen loyal to Shiite cleric Moqtada al-Sadr, which have a strong presence in the Iraqi second largest city.

Heavy fighting broke out between Iraqi security forces and the Mahdi Army Shiite militia earlier on Tuesday.

Iraqi security forces launched a massive security operation against rival Shiite factions and gangs who brought disorder and instability in the city.

A three-day curfew was imposed on the city starting from Tuesday, in addition to the closure of the Iraqi-Iranian border.

The operation came a day after the Iraqi Prime Minister Nuri al-Maliki paid a visit to Basra to restore order in the city where instability was spreading.

Iraqi troops take up positions in Basra in this television grab March 25, 2008. (Xinhua/Reuters Photo)