On Saturday, a roadside bomb killed a US soldier in northwest Baghdad, the 13th to die in the capital this week, the American military announced.
The soldier was struck by the bomb at around 10:30am (0730 GMT), but no more details were given.
The death brings the military's losses in Iraq since the March 2003 invasion to 4,034, according to an AFP tally.
Tanks and drone-launched Hellfire missiles were used to quell attacks on US and Iraqi soldiers, the US military reported on Saturday.
The clashes began when a security force convoy was attacked in Sadr City on Friday night "by multiple roadside bombs, and small-arms fire from adjacent high-rise buildings".
In what the military described as a "complex attack", security forces killed two snipers and two people firing rocket-propelled grenades from a building "where soldiers were taking RPG and machine gunfire".
At the same time, around 9pm local time (1800 GMT), soldiers setting up a checkpoint came under fire from small arms, snipers, machine guns and RPGs after their vehicles were hit by six roadside bombs.
A fierce firefight ensued in which four fighters were killed, the statement said.
Meanwhile, Iraqi authorities ordered residents off the main streets of Sadr City, warning they are littered with bombs primed to explode.
"Groups of people have planted roadside bombs on the majority of the roads of Sadr City," the Baghdad military command said in a statement.
"For the protection of our citizens and media personnel, we are warning people to stay off the streets until they have been cleared by the security forces."
The Sadr City clashes came a day after police imposed a curfew in the city of Najaf in the wake of the killing of a senior aide to al-Sadr near his home.
Riyadh al-Nouri, who was the director of al-Sadr's office in Najaf, was killed as he drove home from Friday prayers in the nearby city of Kufa.
Al-Nouri's death was preceded by fresh US air raids that killed at least 12 people in two of Iraq's main cities, Baghdad and Basra.
|US aircraft have been carrying out air raids |
in Baghdad and Basra in recent weeks [AFP]
Police in Najaf set up blockades, ordered people off the streets and closed shops after the incident, a Reuters news agency reporter said.
The curfew was lifted on Saturday.
Dr Maha al-Duri, a representative of al-Sadr's bloc in Iraq's parliament, blamed the US military for al-Nouri's killing.
"This is one of the conspiracies contrived by the US occupation and their collaborators in Iraq against the al-Sadr movement," she told Al Jazeera.
Also on Saturday, Muqtada al-Sadr said that Robert Gates, the US defence secretary, would always be his enemy because of the continued US occupation of Iraq.
"You have always been my enemy. And you will always be my enemy till the last drop of my blood," Sadr said in a statement.
Gates had reportedly said that those working "within the political process in Iraq" are not the enemies of the United States, referring to al-Sadr's boycott of mainstream politics in Iraq.
"Which political process do you want to involve me in when you are occupying my land?" Sadr said in his statement.
"I heard the statement of the terrorist American defence minister and I feel compelled to give a decent response to such a terrorist. I have no enemy but you. You are the occupier."