U.S. forces pounded parts of Fallujah (search) from the air and ground Thursday, targeting insurgents in a city where American forces were said to be gearing up for a major offensive. Three British soldiers were killed in a bomb attack at a checkpoint in central Iraq.

Al-Jazeera television broadcast a threat by an unspecified armed group to strike oil installations and government buildings if Americans launch an all-out assault on Fallujah. The report was accompanied by a videotape showing about 20 armed men brandishing various weapons, including a truck-mounted machine gun.

The attack that killed the three British soldiers Thursday also left a civilian Iraqi interpreter dead and eight British troops wounded, said Lt. Cmdr. Ahmed Ajala, a British military spokesman in Basra. Six of the wounded soldiers were released from a hospital and the other two were expected to return to their regiment Friday, he said.

British Armed Forces Minister Adam Ingram said in London that the attack was carried out by a homicide car bomber. He said soldiers at the checkpoint also came under mortar fire.

The British soldiers were part of an 850-strong unit who were deployed closer to Baghdad last week to allow U.S. Marines to reposition in Anbar province (search), home of guerrilla strongholds of Fallujah, Ramadi, Hit and Husaybah.

The move from the relatively peaceful sector to the American-controlled zone, where troops come under daily attack from insurgents, carries the risk of higher casualties and is politically sensitive for British Prime Minister Tony Blair (search). The deaths Thursday raise the number of British troops killed in Iraq to 73.

Early Thursday, U.S. aircraft fired on several barricaded militant positions in northeast and southeastern Fallujah, the military said. Later in the day, U.S. artillery batteries fired two to three dozen 155mm shells at insurgent bastions in the city, the military said.

Insurgents and U.S. forces also clashed briefly Thursday in Ramadi, west of Fallujah, but there were no U.S. casualties, the military added.

The fresh action followed overnight fighting on the southeastern outskirts of Fallujah after insurgents fired a rocket-propelled grenade at Marines. Two insurgents were killed while no U.S. casualties were reported, said Lt. Nathan Braden, of 1st Marine Division. Hospital officials in Fallujah reported three civilians were injured in the overnight shelling.

U.S. forces are preparing for a major offensive in Fallujah, west of Baghdad, and other Sunni militant strongholds in hopes of curbing the insurgency ahead of January's election.

An Iraqi National Guard patrol was hit Thursday by a car bomb in Iskandariyah, an insurgent hot spot 30 miles south of Baghdad, killing three people and wounding 15, Iraqi hospital officials said.

A homicide car bomber killed three and wounded nine others when his explosive-laden vehicle barreled into the city government offices in Dujail, 46 miles north of the capital, police said.

On Wednesday, a U.S. soldier was killed and another wounded in a roadside bombing 12 miles south of the capital. A suicide driver detonated his vehicle at a checkpoint near Baghdad airport, injuring nine Iraqis and forcing U.S. troops to close the main route for hours.

Gunmen killed a senior Oil Ministry official, Hussein Ali al-Fattal, after he left his house in the Yarmouk district of western Baghdad, police said. Al-Fattal was the general manager of a state-owned company that distributes petroleum byproducts.

The violence served as a grim reminder of Iraq's rapidly deteriorating security situation, which President Bush must address now that he has been re-elected.

On Thursday, Al-Jazeera aired video of three Jordanian truck drivers taken hostage by a militant group calling itself Jaish al-Islam, or Army of Islam. The men appealed to their country to warn its citizens against working with coalition forces in Iraq, Al-Jazeera said, although their voices were not audible on the tape.

They were part of a convoy of seven truckers who came under attack Tuesday near Fallujah, according to an official at the Jordanian Truckers Association. One of the drivers was killed in the attack, two others are still missing and a fourth man escaped, he said.

More than 170 foreigners have been kidnapped and more than 30 of them — including three Americans and a Briton — killed in Iraq since Saddam Hussein's regime fell in April 2003. At least six of the foreigners were beheaded by followers of Abu Musab al-Zarqawi (search), a Jordanian militant who has sworn allegiance to Al Qaeda.

Another militant group, the Ansar al-Sunnah Army (search), posted a videotape on a Web site showing the beheading of man it said was an Iraqi army major captured in Mosul. The group called Maj. Hussein Shanoun an "apostate" and said he confessed to participating in attacks against insurgents.

Just before his death, Shanoun warned Iraqi soldiers and police against "dealing with the infidel troops," meaning the Americans.

Insurgents have stepped up attacks on Iraq's U.S.-trained security forces, who the Americans hope will assume greater responsibility to enable Washington to begin drawing down its forces — now at their highest levels since summer 2003.

More than 85 percent of the estimated 165,700 multinational troops in Iraq are Americans, despite U.S. efforts to encourage other countries to share the burden.