BAGHDAD, Iraq - U.S. and Iraqi forces sealed off roads to an insurgent stronghold south of Baghdad today and militants bombed two bridges in an apparent bid to hinder troop movement, as pro-government forces tried to retake control of the region ahead of national elections.

On Tuesday, Iraq's Interim Prime Minister Ayad Allawi said the tempo of attacks against insurgent strongholds would increase but acknowledged that the security challenge was a "source of worry."

"I don't want to deny the impact of the security situation nor minimize the size of the challenges we face," Allawi said during a speech in Baghdad. "I believe that many of the Iraqi people agree with me that we should not let terrorist forces decide our agenda."

More than 3,000 U.S. and Iraqi forces on Tuesday launched a major operation to retake control of insurgent-held parts of Babil province - an area notorious for kidnappings and ambushes and home to the fabled city of Babylon.

The Marines and Iraqis punched their way across the Euphrates River, rounded up 160 suspects, seized a suspected training camp and took control of a major bridge, the U.S. command said. The bridge, spanning the Euphrates, is believed to be a favored corridor linking insurgent areas around Baghdad, Fallujah and towns farther south.

Today, U.S. soldiers and Iraqi National Guardsmen were sealing off the roads leading to Qasir town in the Youssifiyah area, preventing anybody from going in or out. A day earlier, insurgents detonated a car bomb in Youssifiyah, 12 miles south of the capital, as the Iraqi National Guard was conducting raids, killing one civilian and wounding 13 Iraqis.

Residents said two explosions - one a car bomb another a roadside bomb - hit two bridges in the area today, in an apparent attempt by insurgents to affect the movement of Iraqi and U.S. forces.

U.S. and Iraqi forces are trying to curb the mounting insurgency in order to hold national elections throughout the country in January. Some U.S. officials have expressed doubt that balloting will be possible in areas that have slipped from Iraqi government control.

"The U.S. military operation is unjustified and most of the arrests are random and it will increase the hostilities in the area," Mohammed Fadhil, the 20-year-old owner of a Youssifiyah grocery shop said today. "The Americans want to stop the resistance which they call terrorism and this is wrong. In fact is it is legitimate reaction to the occupation"

But others felt the raids were needed to restore order in the region.

"I support the military operation conducted by U.S. soldiers and Iraqi national guards. We should get rid of the armed groups in our area because their (the insurgents) only goal is to kill more Iraqis and to ignite civil war," said Mohammed Hussein, 29, a farmer.