BAGHDAD — Anti-American Shiite cleric Muqtada al-Sadr gave a "final warning" to the government Saturday to halt a U.S.-Iraqi crackdown against his followers or he would declare "open war until liberation."A full-blown uprising by al-Sadr, who led two rebellions against U.S.-led forces in 2004, could lead to a dramatic increase in violence in Iraq at a time when the Sunni extremist group al-Qaida in Iraq appears poised for new attacks after suffering severe blows last year.
Al-Sadr's warning appeared on his Web site as Iraq's Shiite-dominated government claimed success in a new push against Shiite militants in the southern city of Basra. Fighting claimed 14 more lives in Sadr City, the Baghdad stronghold of al-Sadr's Mahdi Army.
Fighting in Sadr City and the crackdown in Basra are part of a government campaign against followers of al-Sadr and Iranian-backed Shiite splinter groups that the U.S. has identified as the gravest threat to a democratic Iraq.
Prime Minister Nouri al-Maliki, also a Shiite, has ordered al-Sadr to disband the Mahdi Army, Iraq's biggest Shiite militia, or face a ban from politics.
In the statement, al-Sadr lashed back, accusing the government of selling out to the Americans and branding his followers as criminals.
Al-Sadr, who is believed to be in Iran, said he had tried to defuse tensions last August by declaring a unilateral truce, only to see the government respond by closing his offices and "resorting to assassinations."
"So I am giving my final warning ... to the Iraqi government ... to take the path of peace and abandon violence against its people," al-Sadr said. "If the government does not refrain ... we will declare an open war until liberation."
U.S. officials have acknowledged that al-Sadr's truce was instrumental in reducing violence last year. But the truce is in tatters after Iraqi forces launched an offensive last month against "criminal gangs and militias" in the southern city of Basra.
The conflict spread rapidly to Baghdad, where Shiite militiamen based in Sadr City fired rockets at the U.S.-protected Green Zone, killing at least four Americans. U.S. officials say many of the rockets fired at the Green Zone were manufactured in Iran.
The Iranians helped mediate a truce March 30, which eased clashes in Basra and elsewhere in the Shiite south. But fighting persisted in Baghdad as U.S. and Iraqi forces sought to push militiamen beyond the range where they could fire rockets and mortars at the Green Zone.
The Americans are attempting to seal off much of Sadr City, home to an estimated 2.5 million people, and have used helicopter gunships and Predator drones to fire missiles at militiamen seeking refuge in the sprawling slum of northeast Baghdad.
At a news conference Saturday, Iran's ambassador to Baghdad said his government supports the Iraqi move against "lawbreakers in Basra" but that the "insistence of the Americans to lay siege" to Sadr City "is a mistake."
"Lawbreakers (in Basra) must be held accountable ... but the insistence of the Americans to lay siege to millions of people in a specific area and then bombing them randomly from air and damaging property is not correct," Ambassador Hassan Kazemi Qomi said.
Qomi warned that the American strategy in Sadr City "will lead to negative results for which the Iraqi government must bear responsibility."
At least 14 people were killed and 84 wounded in Saturday's fighting in Sadr City, police and hospital officials said. Sporadic clashes were continuing after sundown, with gunmen darting through the streets, firing at Iraqi police and soldiers who have taken the lead in the fighting.
According to the Interior Ministry, at least 280 Iraqis have been killed in Sadr City fighting since March 25, including gunmen, security forces and civilians.
In Basra, Iraq's second largest city about 340 miles southeast of Baghdad, Iraqi soldiers backed by British troops pushed their way into Hayaniyah, the local stronghold of al-Sadr's Mahdi militia.
As the operation got under way, British cannons and American warplanes pounded an empty field near Hayaniyah as a show of force "intended to demonstrate the firepower available to the Iraqi forces," said British military spokesman Maj. Tom Holloway.
Last month, Iraqi troops met fierce resistance when they tried to enter Hayaniyah. On Saturday, however, Iraqi soldiers moved block by block, searching homes, seizing weapons and detaining suspects.
Lt. Gen. Ali Ghaidan said he expected the whole area to be secured by Sunday. He said troops had detained a number of suspects but refused to give details until the area was cleared.
The fighting in both Basra and Baghdad is part of a campaign by al-Maliki, a Shiite, to break the power of Shiite militias, especially al-Sadr's Mahdi Army, and improve security in southern Iraq before provincial elections this fall.
Al-Sadr's followers believe the campaign is aimed at weakening their movement to prevent it from winning provincial council seats at the expense of Shiite parties that work with the United States in the national government.
Tensions between the Sadrists and other Shiite parties have been rising for months before the Basra crackdown and escalated after parliament last month approved a new law governing the provincial elections.
Clashes also broke out near Nasiriyah, a Shiite city about 200 miles southeast of Baghdad, leaving at least 22 people dead, police said. A curfew was clamped on the town of Suq al-Shiyoukh, where the fighting broke out between police and al-Sadr's followers.
Meanwhile, the U.S. military said an American soldier was killed by a roadside bomb while on patrol in Salahuddin province. At least 4,038 members of the U.S. military have now died since the war started in March 2003, according to an Associated Press count.
Elsewhere in Iraq, at least five people died and 18 were injured in separate bombings in the northern cities of Mosul and Kirkuk and the Diyala provincial capital of Baqouba.
The attacks capped a violent week that has raised concerns that suspected Sunni insurgents are regrouping in the north. U.S. and Iraqi troops have stepped up security operations in Mosul, believed to be one of the last urban strongholds of al-Qaida in Iraq.
On Saturday, a Washington-based group that monitors Islamic extremists said al-Qaida in Iraq has announced a one-month offensive against U.S. troops.
The SITE group said the announcement was made on Web sites by the leader of al-Qaida in Iraq, Abu Ayyub al-Masri, who took over the extremist group after Abu Musab al-Zarqawi was killed in a U.S. airstrike in 2006.