The four, including a child, died when the bomber blew up a Chevrolet Caprice in the main northern city of Mosul, wounding five others, the US military said.

"At approximately 8:02 (0402 GMT) a car loaded with explosives detonated 50 metres (yards) from the main gate of the Mosul airfield," it said.

"One Iraqi civilian and one child were killed when the car exploded. One Iraqi facility protective service employee... later died of wounds. The driver of the vehicle was also killed."

Three US soldiers and two security guards were wounded, the statement added.

A cache of munition rounds loaded inside the car failed to explode, minimising the damage from the blast.

In the main southern city of Basra, two women working at the British-operated airport were shot dead, the latest in a string of attacks on Iraqis working with the foreign troops still stationed across the country.

"Two women were killed and two others wounded when their minibus was attacked in the Mishraq district," a medic at the Sadr teaching hospital said.

Meanwhile, a senior Iraqi police officer at the interior ministry, Colonel Mussab al-Awadi, was shot dead in a Baghdad restaurant Monday, a spokesman said.

"Colonel Mussab al-Awadi was shot in the early afternoon by unknown (gunmen) who opened fire in the al-Baya area in western Baghdad," said the spokesman, refusing to give his name.

The death of Awadi, who had coordinated security arrangements with tribal elders, was the latest in a string of killings of senior civil servants since Iraq's caretaker government was appointed on June 1.

Earlier, a car bomb exploded in Baghdad and at least two mortar rounds were fired at the education and oil ministries, security sources and witnesses said.

"An Opel car bomb exploded near the Sarafia bridge on a road where police make frequent patrols," said fireman Safin Rashid.

The health ministry said later that one person was wounded in the 8:00 am (0400 GMT) attack.