Baghdad, Iraq ? About 3,500 U.S. and Iraqi troops backed by jets launched a major attack Saturday against an insurgent-held town near the Syrian border, seeking to dislodge al-Qaida and its allies and seal off a main route for foreign fighters entering the country.

U.S. officials describe the town of Husaybah as the key to controlling the volatile Euphrates River valley of western Iraq and dislodging al-Qaida in Iraq, led by Jordanian terror mastermind Abu Musab al-Zarqawi.

The U.S.-led operation includes about 1,000 Iraqi soldiers, and the offensive will serve as a major test of their capability to battle the insurgents – seen as essential to enabling Washington to draw down its 157,000-strong military presence.

Thunderous explosions shook Husaybah early Saturday as U.S. Marines and Iraqi scouts, recruited from pro-government tribes from the area, fought their way into western neighborhoods of the town, 200 miles northwest of Baghdad, residents said.

As fighting continued throughout the day, U.S. jets launched at least nine airstrikes, according to a U.S. Marine statement. The U.S. command said there were no reports of casualties among American or Iraqi forces.

People walk among the rubble of a destroyed house Saturday in Baqouba, Iraq. Local residents say the house was destroyed by U.S. troops after a roadside bomb exploded near a U.S. convoy patrolling the area. One civilian died and three were injured, eyewitnesses said.

However, the military said Saturday that three more U.S. troops had been killed elsewhere in Iraq.

One soldier was killed Friday by small-arms fire south of Baghdad, and another died the same day when the vehicle in his patrol was hit by a mine near Habaniyah, 50 miles west of the capital. The third soldier was killed Saturday in a traffic accident in southern Iraq.

Those deaths raised to at least 2,045 the number of U.S. service members who have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

Also Saturday, five Iraqi police were killed and three wounded when a roadside bomb exploded in northern Baghdad, hospital officials said.

And 11 members of a Kurdish Shiite family – including an infant – were killed and three wounded when gunmen sprayed their minibus with automatic weapons’ fire northeast of Baghdad, police said.

The relatives were returning to their home in the Baghdad area after visiting a family cemetery near Balad Ruz, about 50 miles away. Shiite Muslims traditionally pay their respects to their dead during the three-day Eid al-Fitr holiday, which marks the end of Ramadan and ends for most Shiites today.

The attack’s motive was unclear, but tensions between Shiites and Sunnis have been on the rise in the area, with extremists from each community targeting the other.

Elsewhere, a 65-year-old male detainee died Saturday of natural causes at a U.S. military prison camp in southern Iraq, the U.S. military announced. Camp Bucca is located near the southern port city of Umm Qasr near the Kuwaiti border.

U.S. commanders hope the Husaybah offensive, code-named “Operation Steel Curtain,” will restore control of western Anbar province ahead of the parliamentary election Dec. 15 and enable Sunni Arabs there to vote.

Sunni Arabs form the vast majority of the insurgents, and U.S. officials hope that a strong Sunni turnout next month will encourage many of them to lay down arms and join the political process.

However, some Sunni Arab politicians and tribal leaders complained that the Husaybah operation was endangering civilians in the overwhelmingly Sunni area and could lead to greater instability throughout Sunni sections of the country.

“We call all humanitarians and those who carry peace to the world to intervene to stop the repeated bloodshed in the western parts of Iraq,” said Sheik Osama Jadaan, a Sunni tribal leader. “And we say to the American occupiers to get out and leave Iraq to the Iraqis.”

Husaybah, a poor Sunni Arab town of about 30,000 people, is the first stop in a network of communities that the U.S. military suspects al-Qaida of using to smuggle fighters, weapons and explosives from Syria down the Euphrates valley to Baghdad and other cities.