A U.S. soldier also was killed Monday by a roadside bomb in the northern Salahuddin province, the military said, raising to at least 4,033 the number of American military members who have died since the war started in March 2003.
The violence comes as the Iraqi government continues to deal with the failure of a major offensive that began on March 25 to dislodge militia groups from Basra, Iraq's second-largest city.
Iraqi security forces were surprised by the ferocious resistance mounted by the outnumbered militiamen, despite artillery and air support provided by U.S. and British forces.
More than 1,000 security troops - including a full infantry battalion - refused to fight or joined the militias, handing them weapons and vehicles.
The government and police officials announced Sunday that those forces along with some 300 police in the southern city of Kut had beenfor abandoning their posts or refusing to fight.
That decision drew an angry response from al-Sadr, who demanded Monday that the security forces be reinstated.
"All the brothers in the army and police who gave up their arms to their bothers (Sadrists), were only obeying their grand religious leaders and they were driven by their religious duties," the anti-U.S. cleric said.
"I call upon all concerned authorities to reconsider their decision to dismiss those people from the army and the police. I demand they be reinstated and even rewarded for their loyalty and devotion to their religion," he added.
The fighting, which quickly spread to other cities in the southern Shiite heartland and Baghdad, ebbed after al-Sadr ordered a cease-fire but sporadic violence continues.
A commander in the police department's serious crimes directorate, Maj. Ali Haider, was shot to death Sunday night, police said. Haider was a member of the Supreme Islamic Iraqi Council, a Shiite political party that is often at odds with factions loyal to al-Sadr.
U.S. officials have praised Prime Minister Nouri al-Maliki, himself a Shiite, for showing determination in confronting the militias, but they also have said the Basra operation was hastily arranged and badly executed. Critics said it highlighted the Iraqi army's poor leadership and the low morale among its rank and file.
Clashes also continued in Baghdad, where Iraqi and U.S. troops have confronted the Mahdi Army. A large section of a market area in eastern Baghdad was set ablaze early Monday when a bomb exploded next to a convoy of U.S. military vehicles driving down a commercial thoroughfare. The U.S. military said no casualties were reported in the 2 a.m. blast.
Another roadside bomb hit a minibus in downtown Baghdad, killing five passengers and wounding nine, police said.
In northern Iraq, meanwhile, a parked car bomb exploded near an Iraqi army convoy in the Rabiaa area west of Mosul, killing 12 Kurdish soldiers and wounding five, police chief Col. Mutlaq al-Shimmari said.
A suicide bomber also blew himself up during a funeral for a Shiite family in Tal Afar, to the south of Mosul, killing five people and wounding 22, Mayor Najim Abdullah said.
Those attacks came hours after an explosives-laden car blew up in the city itself.
Mosul, 225 miles northwest of Baghdad, is believed to be the last urban stronghold of al Qaeda in Iraq
Elsewhere in Iraq, the military said U.S. soldiers unearthed a mass grave Sunday containing as many as 30 badly decomposed bodies near Muqdadiyah, about 60 miles north of Baghdad.
In other developments: