Armed men in a car drove up alongside a police patrol car in the al-Baladayat district of western Baghdad and sprayed it with bullets, killing two policemen and wounding one.
Half an hour later, armed men in a car shot dead another policeman in a police car in the same district of the capital. Two civilians nearby were also killed, police said.
On Thursday armed men fired on a car carrying Czech police officers deployed in the Iraqi capital to provide security for Czech diplomats, an official said on Friday.
Unknown assailants fired shots at the vehicle on Thursday morning while it was on its way from Baghdad airport, Interior Ministry spokeswoman Radka Kovarova said. She declined to say how many policemen were in the car.
The policemen returned fire and fled the scene, she said. No one in the car was injured.
Meanwhile, only half of Iraq's police battalions are capable of carrying out operations, while two-thirds of army battalions and the rest of the police are no more than "partially capable", according to a US military assessment made public on Thursday.
"Only a small number of Iraqi Security Forces are taking on the insurgents and terrorists by themselves," according to an unclassified assessment provided to the Senate Armed Services Committee by Marine Corps General Peter Pace, vice-chairman of the US military's Joint Chiefs of Staff.
Pace said half of Iraq's police
were partially capable
Pace's assessment was provided to reporters the same day the Pentagon gave lawmakers, more than a week late, a 23-page congressionally mandated report on the status of Iraq on political, economic and security fronts.
The Bush administration has said US forces cannot leave Iraq until American-trained Iraqi security forces are capable of protecting their own country.
Iraqi army limited
Administration officials often cite progress being made by those security forces, which the report said numbered 171,300.
But Pace, poised to become the top US military officer this autumn, told lawmakers only about a third of Iraqi army battalions were capable of planning, executing and sustaining operations against fighters with the support of US-led foreign forces.
"Approximately two-thirds of their army battalions and one half of their police battalions are partially capable of conducting counterinsurgency operations in conjunction with coalition units," Pace's assessment stated.
"Approximately one half of their police battalions are forming and not yet capable of conducting operations."