Colonel Hatim Rashid Muhammad was killed along with an aide during an ambush in Balad Ruz, 50km northeast of the capital.
Aljazeera learnt another police officer accompanying him was also shot dead while they were both on patrol in Balad Ruz, southeast of Baquba.
Balad Ruz lies in the mixed Sunni and Shia Muslim province of Diyala, where fighters frequently attack US-backed security forces.
Fighters have been increasingly attacking the Iraqi police and military, who have taken a larger role in trying to stabilise the country in recent months, supported by about 160,000 foreign troops.
Car bombers mounted two attacks on Iraqi soldiers in northern Iraq on Thursday, killing at least seven people.
There has been a series of targeted assassinations of police chiefs and senior Iraqi military commanders in recent weeks.
Last month, the police chief in a southern Baghdad district was gunned down on his way to work.
And the commander of the Iraqi National Guard in the southern city of Basra was assassinated along with his son while visiting Baghdad.
Gas tanker explosion
A bomber blew up a gas tanker outside a US military base in central Ramadi on Friday, the commander of an elite Iraqi security force stationed in the strife-torn Iraqi city said.
"A gasoline tanker driven by a suicide bomber targeted a US military base in Azud neighbourhood in Ramadi.
"Because we don't have any Iraqi army or commandos on this base, we don't know of any casualties," said General Muhammad al-Azawi.
The US military said it had no record of the attack.
A Romanian television station on Friday showed a new photograph of three Romanian hostages in Iraq, standing and surrounded by armed men.
A fourth hostage, Iraqi-American Mohamed Munaf, who appeared with them earlier, was absent from the photo broadcast by the Realitatea TV network.
Romania is saying little about its
efforts to free the hostages
In the photo, journalists Marie-Jeanne Ion, Eduard Ohanesian and Sorin Miscoci could be seen, flanked by two armed kidnappers and showing the camera their press cards and passports.
They were all wearing the same clothes as in the video, shown on Wednesday on Aljazeera.
Romania has about 800 troops serving in the US-led forces in Iraq.
The Romanian government is saying little about its efforts to free the captives.
"We are making an enormous effort, unprecedented for the Romanian state," Foreign Minister Razvan Ungureanu said.
He called on Romanians to be "patient".
"You will have news when the time is right," Ungureanu said.
Families meet president
The families of the four hostages met in Bucharest on Friday with President Traian Basescu.
Prime Minister Calin Tariceanu had on Thursday said his government would analyse the video to determine how to proceed with negotiations.
"We are making an enormous effort, unprecedented for the Romanian state"
Romanian Foreign Minister Razvan Ungureanu
In Aljazeera's broadcast, two hooded men were seen pointing their weapons at the four visibly frightened hostages, who were seated on the ground against the backdrop of a floral carpet.
Ion, 32, a reporter for Prima TV, her cameraman Miscoci, 30, and Ohanesian, 37, of the Romania Libera newspaper were reported missing by the Romanian foreign ministry earlier this week.