U.S. and Iraqi forces launched a major offensive Saturday along a key part of the Syrian border to combat smuggling of foreign fighters and materials into Iraq and to lay the groundwork for national elections in six weeks, the U.S. military announced.

About 2,500 U.S. and 1,000 Iraqi troops were involved in the Steel Curtain offensive in and around Husaybah, a town of about 30,000 people on the Syrian border about 200 miles west of Baghdad. The U.S. military says the town is a primary transit point and staging area for al Qaeda in Iraq, the country's main insurgent group, led by Jordanian Abu Musab Zaqarwi.

Residents of Husaybah reached by telephone said they were awakened at dawn by four large explosions, followed by announcements over loudspeakers atop U.S. military vehicles that they should immediately leave through the town's northeast entrance. Dozens of families headed that way on foot under white flags, residents said.

A military spokesman said Saturday night that U.S. and Iraqi forces had encountered "sporadic resistance," mostly roadside bombs and small-arms fire.

Residents said that Iraqi insurgents had taken up positions in previously dug trenches, while fighters from Saudi Arabi, Syria, Jordan and Egypt were engaging U.S. and Iraqi troops.

Local hospital officials said there were no immediate reports of casualties. There were no reports of U.S. or allied casualties, either, although the military often delays the release of such information for a day or longer.

A statement purportedly from al Qaeda in Iraq that was posted at a local mosque said the group would retaliate for the offensive in coordination with people in Baghdad and elsewhere.

In other violence Saturday, 11 people, including a 4-year-old boy, were killed at about 7:30 p.m. when gunmen sprayed their minivan with bullets in Baqubah, about 35 miles northeast of Baghdad, police said. And a prominent Sunni Arab, Fakhri Qaisi, spokesman for the National Dialogue Council political group, was reportedly shot five times while driving alone in western Baghdad, the Reuters news agency reported. Physicians treating him said his injuries were life-threatening.

The U.S. military reported that a soldier was killed by small-arms fire south of Baghdad and a Marine died when his vehicle was hit by a roadside bomb near Habbaniyah, about 50 miles west of the capital.

Maj. Gen. Rick Lynch, a senior U.S. military spokesman in Baghdad, said the Steel Curtain offensive was part of a campaign now five months old to stop the infiltration of foreign fighters, money and weapons coming into Iraq from Syria along the Euphrates River valley, which stretches from the border almost to Baghdad.

Anbar province, where Husaybah is located, is one of the few Iraqi provinces where Sunni Arabs make up the majority of the population. It is the main center of the insurgency, and more than a third of all U.S. military fatalities in Iraq have occurred there.

Because of a Sunni Arab boycott and security concerns, only 2 percent of Anbar's voters cast ballots in parliamentary elections in January. About 32 percent voted in a constitutional referendum last month, with more than 96 percent of them opposing the proposed charter, which was approved on the strength of overwhelming Shiite and Kurdish support elsewhere in the country.

The timing of the new offensive -- which came on the final day of Eid al-Fitr, a three-day festival that is one of the holiest holidays of Islam and marks the end of Ramadan -- drew accusations from some politicians and Iraqi citizens that it was culturally insensitive, religiously divisive and politically counterproductive. Some said it could worsen the divisions between the Shiite majority and Sunni Arabs in advance of national parliamentary elections on Dec. 15.

"We think that they are targeting us, the Sunnis, not Qaeda," Omar Obaidi, 45, a government employee, said in a telephone interview as he walked out of Husaybah under a white banner with his wife and three children.

"We are in the third day of Eid. We are leaving the town not for fun but to save ourselves from death," he said. "Instead of having my family for a picnic in an amusement park, I am taking them out of the town, walking and expecting death every moment. Let Bush see how he created a generation that hates the Americans."

"It's against the rule of Islam, against the rule of religion, against the rule of any humanitarian attitude to spoil the festive day for the Iraqis in such a bloody action," said Saleh Mutlak, a Sunni Arab member of Iraq's parliament. "This will make the situation worse. I call on the American people to urge their government to find a civilized attitude. I don't think this fits with the reputation that the Americans have."

Lynch, the military spokesman, said in an interview that with "every planned operation, we take cultural sensitivity and things like holidays into consideration. For the momentum of the operations to continue, the decision was made to conduct the operation this morning, fully conscious of the fact that there was indeed a religious holiday, but knowing that it was important to continue the momentum."

Some analysts have criticized the United States for engaging in several high-profile military offensives, only to withdraw from the areas and allow insurgents to reestablish themselves. Lynch said that would not happen again.

"When there was a shortage of security forces, operations were conducted and people left because there weren't security forces to leave behind," he said. "But when you're in an environment like we're in now, with 211,000 trained and equipped members of the Iraqi security forces, people stay behind to maintain order and discipline."

Correspondent Jonathan Finer in Baghdad and special correspondent Hassan Shammari in Baqubah contributed to this report.

People walk amid the rubble of a house in Baqubah. Residents said the house was destroyed by American troops after a bomb exploded near a U.S. convoy.