An AFP correspondent reported seeing a masked man walk up to a car at a petrol station in Basra on Monday and fire two bullets at the head of the policeman sitting behind the wheel. He tried to shoot a woman next to him, but missed.
Police Lieutenant Amar Hamid confirmed the policeman was killed.
In the northern ethnically divided city of Kirkuk, a member of one of the main Kurdish parties - the Patriotic Union of Kurdistan - was also shot and killed in his car on Monday morning, police there said.
"Shezad Hussain Ali al-Jabari, 28, was shot in the head inside his car on his way back from visiting relatives. There were three attackers and they escaped," said Col Sarhad Kadir.
Also on Monday, a Turkish contractor and two Iraqis were killed in an ambush in the northern city of Tikrit, a spokesman for the US 1st Infantry Division said.
Tikrit police said a third Iraqi was killed in the attack and another Iraqi was wounded.
One Iraqi was killed and another
wounded in the Tikrit attack
The US military spokesman said the men, who worked for a construction company responsible for repairing bridges in Tikrit, were attacked by resistance fighters who opened fire on the contractors' vehicle as they went to work.
Several contractors have been killed in Iraq by fighters attempting to force companies to leave.
Meanwhile, Indonesia has said it was looking into reports that one of its nationals was killed in an ambush in the Iraqi city of Mosul, an incident that would mark the first Indonesian fatality in the Iraq conflict.
"We are still trying to find out. We still have no information on who was killed," said Foreign Ministry spokesman Yuri Thamrin.
Police in Iraq said an Indonesian and two Iraqis were killed and a Filipino was wounded when their convoy was ambushed in Mosul on Sunday.
An Iraqi interpreter said the Indonesian was reportedly employed by German company Siemens to set up a local mobile telephone network. Indonesia's Detikcom news website said he was identified as Fahmi Ahmad.
But a spokeswoman for Siemens Indonesia, Julieta Glasmacher, said the victim was not a Siemens employee.
"From the name we can tell he is Indonesian but he is definitely not a Siemens employee. We don't send people to Iraq," she said.
If the death is confirmed, it would be the first time an Indonesian has been killed in Iraq since the US-led war in March last year.
Indonesia, the world's largest Muslim country, was a strong critic of the invasion.