A US Marine Corps statement said US and Iraqi forces also destroyed a "foreign fighter safe house", killed two foreigners and arrested three others during a raid on Tuesday near the bridges.
A marine statement said F/A-18 jets dropped bombs shortly after midnight on two light bridges near Karabilah, about 300km west of Baghdad.
Karabilah is one of a cluster of towns near the Syrian border, a major infiltration route for foreign fighters heading for Baghdad and other major cities, Iraqi officials say.
They add that al-Qaida in Iraq, led by Abu Musab al-Zarqawi, has taken over parts of the area after local residents fled fighting between tribes supporting and opposing the fighters.
The officials, speaking on condition of anonymity for fear of reprisal, said much of al-Qaim, another town nearby, had been abandoned after weeks of tribal fighting.
US marines operate around al-Qaim but have privately complained they do not have enough American or Iraqi forces to secure the area properly.
Also on Tuesday, US troops handed over military control of the Shia city of Najaf to Iraqi forces, marking a significant transfer of security responsibilities in Iraq.
Najaf is home to Iraq's top Shia
leader Ayat Allah Ali Sistani
By giving Iraqi forces control of a strategic military base on the outskirts of the southern city, US forces were officially relinquishing security command of a major urban centre in Iraq, US commanders said.
"It gives me great pleasure to say the Iraqi army in Najaf can control the area," said US area commander Brigadier-General Augustus Collins, who officially handed over control.
Najaf is home to Iraq's top Shia leader Grand Ayat Allah Ali Sistani.
The city and its province is largely populated by Shia Muslims, and most members of government forces stationed in the region are also Shia.
At the handover ceremony, soldiers of the Iraqi battalion taking control of the city demonstrated their Shia loyalties by chanting "Long live Sistani" and "Saddam is a coward".
On Monday, US marines said al-Qaida in Iraq launched multiple attacks the day before against US and Iraqi targets in Hiyt, 135km west of Baghdad.
Twelve people - including 11 civilians, an Iraqi soldier and three bombers - died in the Hiyt attacks.
Separately, Aljazeera learned from medical sources at Tal Afar hospital on Tuesday that the bodies of seven Iraqis together with 13 injured people had been brought to the facility during the past 72 hours.
"It gives me great pleasure to say the Iraqi army in Najaf can control the area"
US Najaf area commander
US forces set Tuesday afternoon as a deadline for citizens of al-Sarai and Hasan Koi areas to leave their houses, as they plan to launch a vast military operation there, the sources added.
Elsewhere on Monday, armed men seized one of the sons of the governor of troubled al-Anbar province, Mamoun Sami Rashid al-Alwani, officials said on condition of anonymity for fear of fighters' reprisals.
The abduction occurred in the provincial capital of Ramadi, west of Baghdad.