Early in the morning a mortar barrage struck the headquarters of the Iraqi Army 14th Brigade near the Jesr al-Zubair area in western the city, but there was no reports on casualties, a local police source told Xinhua.

Another mortar barrage targeted the Shatt al-Arab Hotel in central the city, where the Iraqi Army operations office based, the source said without providing further details.

The source said that a three-day curfew was imposed on the city starting from Tuesday, in addition to the closure of the Iraqi-Iranian border.

Late on Monday, Brigadier Abdul Karim Khalaf, the head of operations in the Iraqi Interior Ministry, announced that a massive security operation will be launched in Iraq's southern oil hub of Basra, some 550 km south of Baghdad.

The offensive, dubbed "Operation Cavalry Assault", aimed at curbing insurgency and sectarian violence in the city, Khalaf said.

The operation came a day after the Iraqi Prime Minister Nuri al-Maliki paid a visit to Iraq's second largest city of 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)