QAIM, Iraq -- With snipers on rooftops and helicopters hovering overhead, US forces clashed with insurgent fighters yesterday while searching homes in a town near the Syrian border.
In Baghdad, Iraq's oil minister narrowly escaped an assassination attempt when a bomb hit his motorcade.
While US forces pushed ahead with their offensive farther west, fighting erupted in the capital of Iraq's Anbar province, with masked militants attacking an Iraqi patrol and sparking a gunbattle in the streets of Ramadi.
Oil Minister Ibrahim Bahr al-Uloum was headed out of the capital to attend the opening of a rebuilt refinery to the north when the roadside bomb hit his seven-car motorcade yesterday morning, killing three of his bodyguards, the ministry said. Bahr al-Uloum was unhurt.
The assassination attempt came a week after a car bomb at a checkpoint near the Oil Ministry killed at least three ministry employees and seven policemen.
Iraq has the world's third-largest known oil reserves, but the industry has been crippled by war, sanctions during Saddam Hussein's rule, and the anti-US insurgency. Oil production remains limited, curbed by decaying infrastructure and frequent militant attacks on pipelines and refineries.
The violence came less than two weeks before a national referendum on a new constitution. Al Qaeda in Iraq and other groups in the Sunni-led insurgency have launched a wave of violence to wreck the Oct. 15 vote, killing at least 207 people in the past eight days, including 16 US forces.
Bahr al-Uloum vowed that the insurgents would fail and that Iraqis will approve the new constitution. ''All Iraqis are looking forward to saying 'yes' to the constitution . . . By doing so Iraq will usher in a new stage," he said after the attack.
But leaders of Iraq's Sunni Arab minority have rejected the constitution and are trying to defeat it at the polls, saying it will tear the country apart into Shi'ite, Sunni, and Kurdish fiefdoms -- the Sunnis being the weakest.
The US offensive near the western border aims to sweep out Al Qaeda in Iraq insurgents who have made the area a stronghold and used it to bring foreign fighters in from Syria.
The sweep, codenamed Operation Iron Fist, began Saturday in the village of Sadah and has spread to Karabilah and Rumana on the banks of the Euphrates River, 180 miles northwest of the capital.
US helicopters fired rockets at targets in Rumana, where a roadside bomb blew up near an American armored vehicle, sending up a plume of black smoke, witnesses said, but no US casualties were reported.
In Karabilah, troops searched house-to-house for militants, apparently meeting stiffer resistance than in Sadah, which most fighters fled before the US troops moved in.
Marine snipers fired from rooftops and US helicopters flew overhead as the advance was slowed for about an hour by insurgent fire, a CNN journalist embedded with the Marines said.
At one point, about 20 Iraqis fled their homes, including one family -- a mother, father and their child -- who were wounded and bleeding after being hit by flying pieces of concrete, CNN footage showed.
The military said it confirmed at least 21 militants killed, two in fighting Monday and 19 from an airstrike the day before, bringing the three-day total to 57.
No US troops have been killed or seriously injured in the offensive, the military said.
But an American soldier died of wounds suffered from indirect fire Saturday in Ramadi, the military said yesterday. The death raised to 1,936 the number of US military members who have died since the Iraq war began in 2003.
The US military also dismissed as ''patently false" a claim Sunday by Al Qaeda in Iraq that its insurgents had captured two US Marines in the fighting, even as the group issued a claim yesterday that it had killed them.
The military said no Marines had been captured and all its service members were accounted for. ''That Al Qaeda resorts to lies and propaganda demonstrates that theirs is a losing cause," the military said.
In Ramadi, 70 miles west of Baghdad, insurgents attacked an Iraqi army patrol, setting one vehicle on fire and sparking a gunbattle. Gunmen in black hoods were seen carrying machine guns and rocket-propelled grenades in Ramadi's streets, and Iraqi civilians gathered around the two burning Iraqi Army pickup trucks. Some civilians celebrated the destruction by carrying around Iraqi military helmets and a military uniform taken from the wreckage.
But the insurgents appeared to have taken the worst of the fight. Seven gunmen were killed, said Captain Jeffrey Pool, a US military spokesman. No casualties were reported among the Iraqi troops.