About 1,000 U.S. and Iraqi troops pounded targets in ground and air attacks Friday in an area on the Syrian border where insurgents have operated almost unhindered in recent months.

The push by Marines and sailors with Regimental Combat Team 2 of the 2nd Marine Division, in tandem with Iraqi soldiers, "began in the early morning hours aimed at rooting out terrorists, foreign fighters and disrupting terrorist support systems in and around Karabilah," according to a Marine statement.

Marines and Iraqi soldiers battled throughout the day with insurgents in Karabilah, and warplanes dropping precision-guided bombs destroyed three buildings from which insurgents were shooting, another Marine statement said. Four civilians, including two women, were wounded in the fighting, the statement said. No other casualties were reported.

In nearby Qaim, residents said Marines entering the town Friday morning encountered no resistance for about an hour but were then attacked by dozens of armed Iraqis and foreigners. After a three-hour fight, the insurgents were driven off and the Marines controlled the town, witnesses said.

Situated near where the Euphrates River crosses the border between Iraq and Syria, Qaim and Karabilah are among a handful of often-lawless towns where U.S. commanders say foreigners are being funneled from Syria into Iraq to fight the country's new government and the foreign forces that protect it.

Qaim was the scene of a concerted insurgent assault on a U.S. Marine post in April, and on June 11, the Marines launched airstrikes outside Karabilah against insurgents who had erected illegal checkpoints along local roads and were menacing civilians. A third nearby town, Husaybah, has been racked by fighting between foreign insurgents and local tribes in the absence of Iraqi or American security forces, residents have said.

Last month, a week-long U.S. assault called Operation Matador swept through a wide area immediately north of the three towns. Marines conducted house-by-house searches in small villages and patrolled roads in an effort to disrupt what commanders have described as a complex insurgent network that trains foreign fighters and moves them to all corners of Iraq. In many places, however, Marines found mostly women, children and the elderly, along with signs that insurgents had slipped away shortly before the Americans arrived.

In Baghdad on Friday, a car bomb killed four people near a Shiite Muslim mosque on the city's east side. A vehicle driven by a suicide attacker exploded about 50 yards from the mosque, igniting a nearby fuel tanker, said a witness, Abbas Abid, 25.

Police said the bombing was intended to kill worshipers leaving the mosque after Friday prayers. But several people at the scene said they thought the driver was targeting a passing police convoy.

Since Iraq's Shiite-led government took office in late April, insurgents have conducted scores of attacks calculated to inflame tensions among the country's disparate religious, ethnic and political groups. Efforts to bring Iraq's Sunni Arabs, who form the core of the domestic insurgent force, into the political process appeared to bear fruit Thursday when a deal was reached to include more Sunnis in the writing of a new constitution.

Special correspondent Bassam Sebti contributed to this report.