Up to 2500 American soldiers have moved into western Iraq, with the US military saying this is the biggest offensive there against al-Qaida-linked fighters this year.

Four US soldiers died in fighting in western Iraq on Monday, while a British national was detained by Iraqi guards near the border with Saudi Arabia in Najaf province.

The US military said on Tuesday the deaths of the four take to at least 1935 the number of US soldiers killed since the invasion of Iraq in March 2003.

One marine was killed by an improvised bomb in Karabila, near the Syrian border, during a major military operation called Iron Fist, a statement said.

Three soldiers were killed by improvised bombs in Haqlaniya, in the western Anbar province, the US military said.

In fighters' grip

Two months after an attempt to push fighters out of the province, Operation River Gate is intended to stop al-Qaida operating in the city of Haditha and two nearby towns, Haqlaniya and Barwana, and to "free the local citizens from the terrorists' campaign of murder and intimidation", the military said in a statement on Tuesday.

The towns are among several in the Euphrates valley where residents say fighters have taken control, despite frequent offensives by the US forces.

During Operation Sword in August, about 1000 US soldiers fought fighters in Haditha and its neighbouring towns, 200km northwest of Baghdad.

About 2500 US soldiers, along with some Iraqi troops, were taking part in the latest crackdown, making it the biggest of the year in Anbar, the sprawling desert province of western Iraq, the US military said in its statement.

Other incidents

Elsewhere, a US army oil truck has been burnt in a bomb explosion in Biji city, south of Mosul. The truck was among a convoy of US vehicles transferring oil to a nearby US military base.

In Kirkuk, two Iraqi officers have been killed and three others injured after fighters, armed with machine guns, attacked their patrol in al-Askari neighbourhood in Kirkuk city, Iraqi police sources said.

In a separate incident, an Iraqi army officer has been killed after armed assailants attacked his house in Kirkuk.

Syrian border

Separately, about 1000 soldiers have been battling al-Qaida fighters near al-Qaim on the Syrian border, 120km to the west, since Saturday in an operation called Iron Fist.

"There are now two major operations going on simultaneously," a US military spokesman in Baghdad said.

In its statement on Haditha, the military said: "The operation's goal is to deny al-Qaida in Iraq the ability to operate in the three Euphrates River Valley cities and to free the local citizens from the terrorists' campaign of murder and intimidation of innocent women, children and men."

"Haditha is an important crossroads for al-Qaida in Iraq's smuggling activities from the Syrian border. Once in Haditha, smugglers can go north to Mosul or continue on to Ramadi, Falluja or Baghdad. The city is home to approximately 75,000 Iraqis, a vital hydro-electric power plant and 28 schools.
"Coalition and Iraqi forces located in western al-Anbar province have seen a recent increase of al-Qaida in Iraq violence in Haditha."

British national detained

Meanwhile, a British national was arrested by Iraqi border guards near the Saudi border in Najaf province, British and Iraqi officials said on Tuesday.

"We can confirm that a UK national has been arrested by the Iraqi department of border enforcement," a British military spokesman said, adding that the Foreign Office was investigating the arrest, which was believed to have taken place on Monday night.

An Iraqi border guard spokesman in Najaf, Saadun al-Jaabari, said guards arrested "a terrorist group consisting of 10 people, including one British national called Colin Peter, near Mathlum, near the Saudi border".

The other nine were Iraqis from the southern city of Basra, he said.

The group was armed with machine guns and was carrying a video camera, a satellite telephone, and GPS satellite-tracking device, al-Jaabari added.

The British embassy in Baghdad could not immediately be reached for comment.

Green Zone blast

A bomber detonated his booby-trapped vehicle at a checkpoint at the main entrance of Baghdad's Green Zone on Tuesday, killing two Iraqi policemen and wounding five, police said.

The high-security area is home to Iraq's parliament and the US embassy.

The explosion, which sent plumes of black smoke up over the Green Zone, occurred at about 1.20pm at the gate that many Iraqi employees use to enter and leave the area where they work for Iraq's government or for the US and British embassies.

The powerful blast killed two Iraqi policemen and wounded five, said police Lieutenant Mohammed Kheyon. The sound of gunfire was heard after the explosion, but Kheyon said he had no immediate information about that.

People entering the main Green Zone gate have to pass through several checkpoints, and a guard who works there said the bomber raced past the first one, was chased by Iraqi guards and rammed his car into a barrier at the second checkpoint.

The guard spoke on condition of anonymity out of concern for his own safety.

PHOTO CAPTION

US soldiers guard arrested Iraqis during an overnight raid in the city of Tikrit, 170 kms north of Baghdad. (AFP)