A US warplane blasted the residence of Saddam Hussein's half-brother and former head of Iraq's Mukhabarat intelligence service with six "smart bombs," the US military said on Friday.

The results of the attack were not yet known.

Barzan Ibrahim Hasan al-Tikriti lived in the building, which also was an operations centre for the intelligence service, but there was no indication that US-led forces thought the Iraqi president might be with him.

A US military official said the bombing was probably aimed at doing further harm to the already battered command and control system for Iraq's fighting forces. It was not known if Barzan was inside the building.

"The brother is a regime presidential adviser," US Central Command said in a statement from its war headquarters in Qatar.

The target was near the city of Ramadi, 110 km west of Baghdad.

Six Joint Direct Attack Munition, or JDAMs, were dropped on the residence from a single aircraft at 1:45 am local time on Friday.

The fate of the building and its occupants was not known. "Battle damage assessment is ongoing," Central Command said.

The military official said US-led forces had found many instances in Iraq of homes doubling as government installations.

The US has tried at least twice to kill Saddam, once with a missile attack at the start of the three-week war and this week by dropping four 900-kg bombs on a Baghdad building. His whereabouts and condition remain unknown.

Barzan led the Mukhabarat intelligence service from 1979 to 1983 and was Iraq's ambassador to the United Nations from 1988 to 1997.

Reputedly Saddam's "banker in the West" while in the diplomatic post, he has rejected allegations that he helped liquidate Kurds in the 1980s.