At least 18 Iraqi military officers were killed in an ambush on Saturday in the province of Anbar, military sources said.

The commander of the army's Seventh Division as well as the commander of its 28th Brigade and several other high-ranking officers were among those killed in the attack, the sources said. Another 32 soldiers were wounded.

It was not immediately clear why so many senior officers were in an area controlled largely by militants linked to al Qaeda, but some sources suggested they had come to document a recent military victory nearby.

Multiple sources said three suicide bombers wearing explosive belts detonated themselves among the officers inside a deserted house in the western town of Rutba, 360 km west of Baghdad.

"All that we know so far is three suicide bombers wearing explosive vests came from nowhere and detonated themselves among the officers," a military officer who was at the scene told Reuters by phone.

Prime Minister Nuri al-Maliki ordered troops in the area to launch an operation to pursue the militants who carried out the attack, the sources said.

No group immediately claimed responsibility, but suicide bombing is the trademark of al Qaeda's Iraqi affiliate, which merged this year with its Syrian counterpart to form the Islamic State of Iraq and the Levant.

Al Qaeda-linked militants have intensified attacks on the security forces, civilians and anyone seen as supporting the Shi'ite-led government, tipping Iraq back into its deadliest levels of violence in five years.

In a separate incident, the commander-in-chief of the police force in Shirqat, 300 km north of Baghdad, was killed and four of his officers were wounded when a roadside bomb exploded by his convoy, police and medical sources said.-Reuters