Another car bomb exploded in the northern city of Mosul in the path of a US convoy. There was no immediate word on casualties.
"Today in the morning hours, al-Budair police chief Colonel Ghaib Hadab Zarib was killed," the military said in a statement on Friday.
"His body was found near his house. The unknown attackers shot at him using an AK-rifle."
Al-Budair is 45km east of Diwaniya in south-central Iraq, where Polish forces are deployed.
An Iraqi civilian was killed and three were wounded when a car bomb parked on the street in Baquba, 60km northeast of Baghdad, exploded about 3pm (1200 GMT), a police source said.
In Mosul, a car bomb parked on the side of a freeway was detonated when a US military convoy passed by at about noon (0900 GMT), witnesses said.
"I saw people come and park the car and then they got into an Opel that was waiting and sped away," said Mohammed Jassim Abdullah, a guard at a nearby riverside park.
There was no immediate comment from the US military on any casualties among its forces.
The explosion left a big hole on the road's shoulder, and remains of the vehicle were strewn everywhere, an AFP correspondent at the scene reported.
In Baghdad, a series of explosions that appeared to be a mortar attack rocked the northern side of the city at about midday and the bridge connecting the Sunni Adhamiyah district with Shiite Khadimiyah on the east bank was blocked with rocks.
Appeal for hostages' release
Meanwhile, a French Muslim leader called on Friday for the immediate release of journalists held in Iraq, including a French reporter who pleaded for her life in a video tape released this week.
"We call for the immediate release of Florence Aubenas and Husain Hanun al-Saadi (her Iraqi interpreter)," Muhammad Bishari, vice-president of the French Council for the Muslim Faith (CFCM), said in Amman.
"We tell the Iraqi resistance that they should not be mistaken about who they are fighting. France has always been on the side of human dignity and the right of people to self-determination," he said.
Bishari, who also called for the release of Italian journalist Giuliana Sgrena, said he will repeat the appeal later on Friday at a conference on Arab-European dialogue and human rights that he is attending in Jordan.
"Abductions are not part of our Arab and Muslim traditions, particularly when the victim is a woman who should be well-treated.
Florence Aubenas disappeared in
Baghdad on 5 January
"Arab and Muslim public opinion will never forgive such an irresponsible act," he added.
Aubenas, a reporter for the French daily Liberation, disappeared in Baghdad on 5 January with her Iraqi interpreter. Sgrena, who works for the Italian daily Il Manifesto, went missing in the Iraqi capital on 4 February.
Bishari was among a CFCM delegation that visited Baghdad in September to try to secure the release of French reporters Christian Chesnot and Georges Malbrunot, who were freed in December, four months after their abduction.
In a separate development, Iraq's Shia and Kurds were planning on Friday to intensify their bargaining over the shape of the next government, one month after the country's elections.
The Shia political bloc, the United Iraqi Alliance (UIA), with 140 seats in the new 275-member National Assembly, is negotiating with the Kurdish Alliance, whose 77 votes make it the second largest party.
"There are almost daily meetings and they are going to be
intensified," said Husain Shahrastani, a senior UIA member and confidant of revered Shia spiritual leader Grand Ayat Allah Ali al-Sistani.
"There is understanding on a number of issues. There is
progress." Shahrastani said there was hope for a deal within a few days.
Also on Friday, US troops imposed a blockade around Barwana district, west of Haditha city, which has been under siege by US troops for the past five days after a missile attack targeted government buildings used by US soldiers.