Iraqi security forces battled Shi'ite militants in Basra yesterday in a drive to win control of the southern oil city, but violence and unrest spread to Baghdad and other cities.
Police and health workers said at least 12 people were killed in the fighting in districts of central and northern Basra where Shi'ite cleric Moqtada al-Sadr's Mehdi Army has a strong presence. The commander of Iraqi forces in the operation said only that "many outlaws" had been killed.
Cleric Sadr, an influential leader who has not been seen in public for months, issued a statement calling on Iraqis to stage sit-ins all over Iraq and said he would declare "civil revolt" if attacks by US and Iraqi forces continued.
The Iraqi government said the operation aimed to win control of Basra, whose vast oil fields provide most of Iraq's revenues, from militias and criminal gangs who dominate the semi-lawless city of about two million people.
"This operation will not come to an end in Basra without the law prevailing and being respected," government spokesman Ali al-Dabbagh said after Prime Minister Nuri al-Maliki arrived in Basra to personally oversee the operation.
The operation, which began at dawn and involved thousands of Iraqi troops, focused on Cleric Sadr's anti-US Mehdi Army in northern and central Basra.
By nightfall, many towns and cities across southern Iraq were under curfew as authorities sought to prevent further outbreaks of violence that threaten Iraq's fragile security.
Clouds of black smoke rose above Basra and explosions and gunfire could be heard throughout the day. Reuters Television pictures showed gunmen firing mortars in the street, while others drove around in captured Iraqi army and police vehicles.
"Bullets are coming from everywhere and we can hear the sound of rocket explosions. This has been going on since dawn," Basra resident Jamil told Reuters by telephone as he cowered in his home earlier in the day.
The operation provoked a furious reaction by the Mehdi Army in Baghdad and in other cities in southern Iraq, with fighters taking to the streets and clashing with police. The militia has grown frustrated with a ceasefire imposed by Shi'ite cleric Sadr last August.
Sadrists say the truce has been abused by US and Iraqi forces to make indiscriminate arrests ahead of provincial elections due in October, but the US military says it only targets "rogue" members who have ignored the ceasefire.
The US military, which once called the Mehdi Army the greatest threat to peace in Iraq, says the seven-month-old ceasefire is one of the main factors contributing to a 60 per cent drop in violence in Iraq since last June.
Police sources said Shi'ite cleric Sadr supporters seized control of five districts in the southern town of Kut after clashes between gunmen and police. Mehdi Army fighters also battled police in two neighbourhoods in the centre of the southern town of Hilla.
In Baghdad, US and Iraqi forces sealed off the Mehdi Army stronghold of Sadr City, a sprawling slum of two million people, after the militia ordered police and soldiers off the streets.
Police said Mehdi Army fighters clashed with gunmen from the Badr Organisation, the armed wing of the rival Shi'ite Supreme Islamic Iraqi Council (SIIC).