A police official said a dozen people were killed north of Baquba on Wednesday when armed men ambushed a minibus carrying employees of an electricity company, spraying it with bullets.
"After the attack, the police came to investigate, and at that time the bus exploded, wounding a policeman," he added.
In a separate incident near Baquba, Kanan Abdallah, Baquba's deputy police intelligence chief and his two bodyguards were shot dead by gunmen, police said.
In Baghdad, a defence ministry media official, Mohammed Moshib, has been killed in an ambush, a source in the ministry said.
Talabani: More than 1,000 people
were killed in Baghdad last month
Also on Tuesday the number of people killed by a truck bomb in a Tal Afar market rose to 24, police said, with the US military putting the wounded at 134.
Jalal Talabani, the president, said at least 1,091 people had been killed in Baghdad alone last month.
"We are shocked and angry at the daily reports of unidentified bodies being discovered and of people killed on the basis of their identity," he said.
Thousands of bodies have been discovered across Iraq, mostly of Sunni Arabs, killed in Shia reprisals after the Samarra bombing.