Armed men in a red sedan shot and killed a policeman in central Falluja, 65km west of Baghdad, at about 9am on Saturday as he was heading to work, according to Lieutenant Sami Muhammad.
Elsewhere, a US Marine helicopter fired two rockets on Saturday into a hideout of anti-government fighters in the western city of Ramadi, killing six of them and wounding another, a marine spokesman said.
A spokesman for the Iraqi army was shot to death in British-controlled Basra, a southern city that has also been noted for its relative stability.
Captain Makram al-Abbasi was killed in a hail of gunfire from a civilian car, also accompanied by a police vehicle in central Basra's Jubaila area, said police Captain Firas al-Tamimi.
Al-Abbasi, a Sunni Arab, had been co-ordinating media coverage of raids conducted in the city, which is the main target for suspect Shia militiamen.
Sunni Arabs have long claimed that Iraq's police forces have been infiltrated by Shia militia members.
In Baghdad, unidentified assailants killed police Sergeant Bassam al-Rikabi while he patrolled in the southeastern Jisr Diyala area at about 11.30pm, police said.
Al-Jaafari is hoping to retain his
position as prime minister
In Baghdad, a Sunni Arab tribal leader, Shaikh Osama al-Jadaan, said his followers have seized more than 1400 "terrorists" in a three-month operation that began about a month ago along the Iraq-Syria border.
"This campaign aims at restoring security on the Iraqi-Syrian borders until the formation of the government and in assisting Iraqi forces to take control of Anbar," al-Jadaan said.
US authorities have recruited scouts, known as Desert Protectors, from among al-Jadaan's tribe in an effort to stop foreign fighters from infiltrating from Syria.
The killings underlined Iraq's continuing lack of security, as members of the Shia alliance who won seats in the 15 December parliamentary elections failed to overcome differences on Saturday on the choice of a prime ministerial candidate.