The recruits were from the largely rural tribal area not far from Abu Ghraib, and part of an effort to get Sunni tribesmen into the security forces to combat Iraq's insurgency, a Fallujah police officer told AFP.

Insurgents frequently target recruiting centres for Iraq's fledgling police and army.

Five more US soldiers have been killed in attacks in Baghdad and the restive western province of Anbar, the US military reported on Friday.

One soldier was killed and two were wounded south of Baghdad on Friday when their patrol was hit by a roadside bomb.

Roadside bombs also claimed the lives of a soldier patrolling predominantly Shia east Baghdad on Thursday and another as in the mostly Sunni western half of the turbulent capital city.

Two soldiers were killed during combat operations in the restive province of Anbar, also on Thursday.

al-Qaeda in Iraq released a recording yesterday purportedly of its leader, who had been reported killed in recent fighting, criticising the country's largest Sunni party and branding its chief, Vice President Tariq al-Hashemi, a "criminal" for participating in the government.

The statement by Abu Hamza al-Muhajir, also known as Abu Ayyub al-Masri, was seen as a warning to Sunnis not to take part in the political process that could legitimize the Shia-led government and its US backers.

Al-Hashemi has resisted calls by fellow leaders of the main Sunni alliance to pull out of the government.

Meanwhile, violence persisted throughout Iraq.

Residents and police in a Shia area in eastern Baghdad said US helicopters early Saturday fired on three houses, killing six men and wounding a woman and five children. The US military said a helicopter supporting ground operations in the area was attacked with small-arms fire but "did not return fire."

AP Television News footage showed a shattered wall of one house and a satellite dish punctured by large holes apparently caused by artillery. Dozens of people marched in a funeral procession for four of those killed, bearing their bodies in wooden coffins draped with Iraqi flags.

Authorities in northern Iraq found the bodies of seven murdered plainclothes policemen in the oil refinery town of Baiji as three people died in a series of attacks on Saturday.

The bodies of the policemen, which were riddled with bullets, had been dumped on the roadside.

The bullet-riddled bodies of the police officers, who were dressed in civilian clothes, were discovered late Friday outside the city of Beiji, 260km north of Baghdad, police said.

Their identity documents showed they were from the turbulent city of Ramadi, police said, and their killing underscored the danger facing Iraqi police in the area, where insurgents routinely target Iraqis seen to be working with the US-led military forces.

In all, at least 25 people were killed or found dead in scattered violence. Those included a policeman killed in a suicide car bomb attack and a woman who died in a mortar attack in Baghdad, as well as three people killed in clashes between Shia and Sunni militants north of the capital.

In southern Baghdad, US soldiers on a routine patrol Friday searched a suspicious blue tanker truck and discovered it had been converted into a large truck bomb, the military said.

The explosive on the truck consisted of 14 155 mm artillery shells and was destroyed by a team of bomb disposal experts, the military said Saturday.

In an effort to prevent further attacks on troops, US-led forces arrested suspected Shia militants accused of smuggling powerful bomb components from Iran during a raid Friday in Baghdad's teeming Shia district of Sadr City.

A US military statement said the militants were part of a "secret cell" that smuggles powerful bombs known as "explosively formed penetrators," or EFPs, from Iran and sends Shia fighters from Iraq for training in Iran.

US and some Iraqi officials suspect the Iranians may be stoking a growing power struggle among Shia factions and political parties despite the Tehran government's insistence that it is working to help bring stability to its neighbor Iraq.