A police official said soldiers were killed in the attack.
A car loaded with vegetables exploded when the patrol approached, the official said.
Earlier that day, armed men fired on customers in a bakery in eastern Baghdad, killing nine people, police said.
The assailants drove up in two cars and burst into the Happiness Bakery. Seven of the victims died in the bakery and two others died in hospital, police said.
But according to some neighbourhood residents, the death toll from the attack was 11.
A police officer said he thought the attack was caused by a conflict between two factions or tribes. A police station opposite the store was not damaged.
One witness said the same bakery was attacked a few weeks ago in a similar manner and three people were killed.
The town of Salman Pak remained sealed off by US and Iraqi troops on Friday after battles with fighters left dozens dead and scores wounded.
Raids by government security forces appear to have triggered the battle.
Armed men fired on the
Happiness Bakery on Friday
"According to our latest toll there were 10 police killed and 75 wounded," a Salman Pak police officer said. He added that 46 police vehicles were destroyed.
National Security Adviser Qasim Daud said that 20 fighters had been killed and 21 arrested.
The figures were later revised to 17 policemen killed and about 80 wounded.
"We have never seen such fighting," said the police officer in Salman Pak.
Several police patrols were sent to Salman Pak on Thursday to carry out raids in a region that has become a trap for security forces and government convoys.
The police officer said fighters retaliated "with a panoply of arms including rocket launchers, mortars and machine guns". The police station was surrounded and attacked with rockets.
A police source said officers inside the building made a plea for US help.
US soldier killed
In related violence, the US Department of Defence announced that a Task Force Baghdad soldier was killed by an improvised explosive device (IED) in western Baghdad on Friday.
No other details were provided.
The defence secretary made a
surprise visit to Mosul
Meanwhile, US Secretary of Defence Donald Rumsfeld flew into Iraq on Friday to inspect US-trained Iraqi security forces.
Rumsfeld arrived before dawn at an airfield outside Mosul. It was his eighth visit to Iraq.
"The task ahead for us is to continue to help the Iraqi security forces to get on the job. That will take some time," Rumsfeld told American soldiers in Mosul.
"It's their country. It's their responsibility. And they're the ones who have that obligation," he said.