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.
The US military said its forces in Sadr City killed seven "criminals" -- two in gunbattles and five in two separate airstrikes. The military said it does not engage if civilians are spotted in the area.
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 US military said an American soldier was killed by a roadside bomb while on patrol in Salahuddin province. The military did not release the soldier's name, pending notification of family.
The military also said Saturday that an Army Special Forces soldier was killed by a burst of small-arms fire while trying to capture an al-Qaida leader in an Iraqi town.
Staff Sgt. Jason L. Brown, 29, was killed early Thursday during a combat operation in Sama Village, the US Army Special Operations Command said in a statement.
At least 4,039 members of the US military have now died since the war started in March 2003, according to an Associated Press count.