QAIM, Iraq -- US troops battled insurgents hiding out in houses and driving explosives-laden vehicles in a town near the Syrian border yesterday, killing 28 in an expansion of their two-day-old offensive chasing Al Qaeda fighters along the Euphrates River valley, the military said.
Al Qaeda in Iraq said it took two Marines captive during the fighting and threatened to kill them within 24 hours unless all female Sunni detainees are released from US and Iraqi prisons in the country. The US military said Al Qaeda's assertion seemed false.
''There are no indications that the Al Qaeda claims . . . are true," said Multinational Force West, the command in the region. Command officials added they were conducting checks ''to verify that all Marines are accounted for."
Even as the fighting continued, political differences among Iraqi leaders deepened ahead of the crucial Oct. 15 national vote on a new constitution. Iraq's Kurdish president, Jalal Talabani, called on the Shi'ite prime minister to step down over accusations he is monopolizing power in the government and ignoring his Kurdish coalition partners' demands, a spokesman for Talabani's Patriotic Union of Kurdistan said.
The US military says Al Qaeda in Iraq, the country's most fearsome insurgent group, has turned the area near the border into a ''sanctuary" and a way station for foreign fighters entering from Syria.
In Karabilah, Marines clashed with insurgents who opened fire from a building yesterday in a firefight that killed eight militants, the military said.
The move into Karabilah widened the sweep launched a day earlier by 1,000 Marines, soldiers, and sailors, starting with nearby Sadah -- a tiny village about 8 miles from the Syrian border.
Most of the militants appeared to have slipped out of Sadah before the force moved in, and hundreds of residents from the village fled into Syria ahead of the assault.
There was ''virtually no opposition" in Sadah, said the Marine commander in western Anbar Province, Colonel Stephen W. Davis.
Davis said at least 28 militants were killed in fighting yesterday, bringing the two-day toll among insurgents to 36. There have been no serious US casualties in the operation, he said.
US forces are aiming to clamp down on insurgents ahead of the Oct. 15 vote. Al Qaeda in Iraq and other groups in the Sunni-led insurgency have launched a wave of violence to wreck the vote, killing more than 200 people over the past week.
The US operation in the Syrian border region is the fourth since May. But US troops are too scattered and Iraqi forces too few to impose permanent control in the area, which is the size of West Virginia.
Militants have fled past assaults only to move back in once the bulk of US forces leave.
Davis said the latest offensive would at least dislodge militants enough to allow residents of the region to vote on Oct. 15 -- and could strike a heavy blow to Al Qaeda in Iraq.
''There's only so many of them out there," Davis said of the insurgents. ''The enemy has a problem out here -- every time he shows up, he gets bombs dropped on his head. . . . What you're seeing now is the dissolution of their network."
In Karabilah, militants forced their way into a building and began firing on Marines, and a US tank fired a round into the building, wounding five civilians, the military said. Marines treated four of them for minor injuries and evacuated the fifth for treatment, it said.
Marine aircraft struck a group of seven insurgents between Karabilah and Sadah, killing four. The others ran into a nearby building, joining other fighters who opened fire on Marines. Warplanes then hit the building with six precision-guided bombs, the military said. In the same area, a suicide car bomber approached a Marine position but detonated 200 yards away, it said.
Elsewhere, Shi'ite militiamen freed the brother of Iraq's interior minister from kidnappers who snatched him from his car a day earlier, the freed man, Abdul- Jabbar Jabr, told Associated Press Television News.
Sunni Arab leaders, meanwhile, cried foul when the Shi'ite-dominated parliament passed new rulings on the upcoming referendum that will make it more difficult for Sunnis to defeat the constitution at the polls.
The parliament's move could undermine US efforts to garner Sunni Arab support for the constitution. It could further alienate moderate Sunnis who say they want to participate in the political process but reject the draft constitution, which they contend will fragment Iraq among majority Shiites, the Kurds, and Sunni Arabs.