Adnan al-Dulaimi said on Friday that 10 Humvees circled his western Baghdad home, then US soldiers went through the building with a dog.

"I condemn this act and I demand they free the guard [Khudhir Farhan]," al-Dulaimi said, adding they had the "illusion ... of the guard's involvement with terrorist activities".

US military spokesman Lieutenant-Colonel Barry Johnson said he had "no reason to dispute his claims" that US forces raided his house, but that he could not comment further on "our ongoing operational activities".

"They found nothing," al-Dulaimi said.

Curfew in Baghdad

In another development, Iraq declared a curfew on Saturday in the capital Baghdad, ordering all cars off the streets and telling people to remain in their homes.

A statement from al-Maliki's office on Friday said the curfew would remain in force until 0200 GMT on Sunday. It gave no reason for the measure.

US commanders say Baghdad has seen a surge in violence in the past week with the beginning of Ramadan.

Clashes and bombings have been frequent during the holy month.

'Difficult thing'

Meanwhile, the commander of US forces in Ramadi, capital of volatile Anbar province, said the armed anti-government campaign can be beaten but probably not until after US troops leave Iraq.

"An insurgency is a very difficult thing to defeat in a finite period of time. It takes a lot of persistence - perseverance is the actual term that we like to use," Army Colonel Sean B MacFarland, commander of 1st Brigade, 1st Armoured Division, said in a video-teleconference with reporters at the Pentagon.

"Who knows how long this is going to actually last?" he added. "But if we get the level of violence down to a point where the Iraqi security forces are more than capable of dealing with it, the insurgency's days will eventually come to an end. And they will come to an end at the hands of the Iraqis, who, by definition, will always be perceived as more legitimate than an external force like our own."

A UN report released on Wednesday said fewer foreign fighters have been killed or captured in Iraq in the last few months, suggesting that the flow of foreign fighters into Iraq "has slackened".

Bush-Maliki talk

Also on Friday, George Bush, the US president and Nuri al-Maliki, the Iraqi prime minister, discussed the security situation in Iraq and efforts to pacify Baghdad in a telephone conversation.

Following the Friday meeting, Bush's spokesman Tony Snow said: "The president reiterated his commitment to the prime minister and the democratically elected government of Iraq.

"The prime minister expressed his confidence in the president and his relationship with the United States."

Bush wrapped up the call by offering al-Maliki his "best wishes" for the Muslim holy month of Ramadan.