Iraqi police say two policemen have been killed and two others wounded in a drive-by shooting in the northern city of Kirkuk.
Authorities say the unidentified gunmen escaped after the attack early Tuesday.
Insurgents have frequently targeted Iraqi police and other officials working with the U.S.-led coalition.
On Monday, two Iraqi civilians were killed and several others wounded when a car bomb exploded outside an American air base north of Baghdad, and two Finnish businessmen were gunned down in the Iraqi capital.
Meanwhile, Iraq's leading Shi'ite cleric, Grand Ayatollah Ali al-Sistani is urging the United Nations not to endorse the country's interim constitution that was signed by the U.S.-appointed Iraqi Governing Council two weeks ago.
In a letter to the U.N. envoy to Iraq, Lakhdar Brahimi, the ayatollah warned that if the Security Council endorses the document, he will not take part in meetings with a U.N. team due in Iraq soon for talks on the formation of an interim government.
The influential Shi'ite leader's statement, made public Monday, comes a little more than three months before Iraqis are scheduled to take over power from the Coalition Provisional Authority.
The interim constitution is designed to guide the country through a transitional period until national elections are held by the end of January and a permanent constitution is drawn up.
Some information for this report provided by AP, Reuters and AFP.