Moqtada al-Sadr's militiamen battled troops in four Iraqi cities on Tuesday, including the capital, as the hardline Shiite cleric threatened a countrywide campaign of civil revolt.
Heavy clashes broke out between Sadr's Mahdi Army fighters in the southern oil city of Basra, killing at least seven people and wounding 48, and in Kut and Hilla, both south of Baghdad, officials said.
As evening fell, Mahdi Army fighters fought with Iraqi and US forces in their Sadr City bastion in eastern Baghdad for the first time since last October, a security official and witnesses told AFP.
Troops had surrounded the sprawling impoverished neighbourhood of two million people and armed Shiite fighters were roaming the streets, a witness said.
The fighting, which severely strains a ceasefire declared by Sadr in late August and renewed last month, prompted the cleric to issue a stern warning that he would launch protests and a nationwide strike if attacks against his movement and "poor people" are not halted.
"We demand that religious and political leaders intervene to stop the attacks on poor people. We call on all Iraqis to launch protests across all the provinces.
"If the government does not respect these demands, the second step will be general civil disobedience in Baghdad and the Iraqi provinces," Sadr said in a statement read by his representative Hazam al-Aaraji in the holy city of Najaf.
Liqa al-Yassin, an MP from the Sadr bloc, told AFP that the Sadrists would boycott parliamentary proceedings "until the government agrees to our demands."
"We are also starting a signature campaign to express no confidence in (Prime Minister) Nuri al-Maliki's government," he said.
Fighting raged from early morning in areas of Basra controlled by the Mahdi Army as troops and police launched a major crackdown on armed groups in the oil hub, considered the nerve centre of Iraq's national economy.
At least seven people were killed and 48 wounded, among them dozens of members of the Iraqi security forces, according to police and medics.
An AFP correspondent said fighting in Basra died away late afternoon and the streets were empty even of security force vehicles.
Clashes raged sporadically in Kut as militants fought Iraqi and US forces but there were no immediate reports of casualties. At least two people died in the Hilla clashes, security officials said.
In August, Sadr ordered a ceasefire following bloody fighting in the shrine city of Karbala blamed on his fighters, which were involved in two rebellions against US forces in 2004.
While Iraqi and US officials say most members of the militia have heeded the order, a number of what the US military terms "rogue elements" continue to attack American forces with mortars, rockets and roadside bombs.
Despite the ceasefire, Mahdi Army members are being subject to raids by the "occupiers" and Iraqi forces which are "destroying Iraqi houses," Sadr's statement said.
"Iraqis in general and Mahdi members in particular are paying the price."
British military officials said Prime Minister Nuri al-Maliki was in Basra to personally oversee the major security force sweep in Iraq's second largest city, but that British troops were not taking part.
An AFP correspondent said fighting involving mortars, machine guns and assault weapons erupted soon after the security forces entered the Al-Tamiyah neighbourhood, a bastion of Sadr's Mahdi Army militia, at around 5:00 am (0200 GMT). The fighting quickly spread to five other Mahdi Army neighbourhoods.
Television pictures showed Iraqi troops running through the streets firing weapons and taking cover as ambulances raced past. Thick palls of smoke were seen rising above the city skyline.
In the wake of the fighting police also imposed curfews in five central-southern Shiite cities -- Kut, Samawa, Nasiriyah, Hilla and Diwaniyah -- as well as in Sadr City.
Basra province was handed over to Iraqi control by British forces in mid-December.
It has since become the theatre of a bitter turf war between the Mahdi Army, the Badr organisation allied to the Supreme Iraqi Islamic Council (SIIC) of powerful politician Abdel Aziz al-Hakim, and the smaller Shiite party, Fadhila, ahead of provincial elections in October.
After touring Basra on Monday, Maliki vowed his government would restore order, saying the city was experiencing a "brutal campaign" by internal and external groups targeting "innocent men and women."
"The federal Iraqi government... will restore security, stability and enforce law in this city."