Insurgents blew up four US marines in Iraq's Anbar province, marking one of the deadliest attacks against US troops in the former Sunni rebel bastion in months, the military said yesterday.

In Sadr City, the Baghdad stronghold of anti-American Shia cleric Moqtada al-Sadr, at least 10 more people were killed in overnight clashes, security officials and medics said.

The marines died when their vehicle was hit by an improvised explosive device on Friday, the US military said in a statement, without specifying the exact location of the attack.

The attack came 10 days after a similar ambush in the province in which two US marines were killed and three wounded.

Friday's attack brought to 1,290 the US military's losses in Anbar since the March 2003 invasion, according to independent website www.icasualties.org, closely trailing the 1,298 killed in the capital Baghdad.

Most of the US dead in Anbar, the biggest province in Iraq, have been due to roadside bombs.

The losses in Anbar make up nearly a third of the 4,071 US troops killed in the conflict so far.

The vast desert province that borders Saudi Arabia, Syria and Jordan was a key stronghold of the anti-US insurgency in the first years after the overthrow of Saddam Hussein'* regime.

Its provincial capital of Ramadi and the nearby city of Fallujah became symbols oi Sunni Arab resistance to US forces in Iraq.

In one of the fiercest battles of the war so far, US forces virtually razed Fallujah to the ground in November 2004 in a devastating offensive to recapture the city from insurgents.

That month saw 137 US troops killed across Iraq -- the highest monthly figure till now -- most of them in theFallujah battle.

According to

www.icasualtics.org, US losses in Anbar peaked in 2006 with 356 service personnel killed.

But violence in the province fell dramatically last year as Sunni Arab tribes fell out with al-Qaeda and joined the US-led war against the jihadist network which had made Anbar one of its bastions

The policy of recruiting former insurgents to the battle against al Qaeda saw US losses in Anbar fall to 161 last year, prompting its extension to other restive provinces

across Iraq.

Overall US losses in Iraq last year totalled 901. That figure compares with 486 deaths in 2003,849 in 2004, 846 in 2005 and 822 in 2006.

So far in 2008, 166 troops have been killed.

In the latest fighting in Sadr City, at least 10 people were killed in overnight crossfire between US troops and Shia militiamen, Iraqi officials said.

Another 17 people were wounded in the violence, security officials and medical sources said.

There was no immediate word from the US military on the latest casualties in the sprawling district where US troops have been fighting running battles with Shia militiamen since March 25.

On Saturday, the US military said it destroyed a command and control centre operated by militants in Sadr City. Witnesses said a shack had been reduced to rubble and a nearby hospital suffered serious damage.

Since then hundreds of people have been killed and followers of Sadr have accused the US military of killing civilians.

The US military charges that the militiamen have been using civilians as human shields.