US forces launched their second major offensive in western Iraq in as many days on Saturday, ratcheting up the hunt for rebels and weapons in the Euphrates river valley that stretches to the Syrian border.
Faced with slipping poll numbers, President George W. Bush asked Americans to show patience, saying that since US troops overthrew Saddam Hussein, Iraq had become a "central front in the war on terror" and a "vital test" for US security.
Around 1,000 US Marines and soldiers, supported by Iraqi troops and backed by fighter jets and helicopters, launched Operation Dagger in the desert about 75 km (50 miles) northwest of Baghdad early on Saturday, the military said.
"Dagger is focused on locating hidden weapons caches and denying insurgents sanctuary," said Captain Jeff Pool.
The new offensive comes after Friday's launch of Operation Spear around the towns of Karabila and Qaim, about 20 km (12 miles) west of the Syrian border, an area US forces believe has become a conduit for foreign militants and weapons.
The military said about 50 insurgents had been killed in air strikes over the past two days, with three Americans wounded. Iraq's al Qaeda group, led by Jordanian Abu Musab al-Zarqawi, said no insurgents had been killed in the strikes.
"They are lying ... their bombs fell on the Muslim public," the group said in a statement posted on an Islamist Web site.
US commanders blame foreign Islamists like Zarqawi for some of the deadliest attacks of the insurgency. They say he may be hiding in the western desert, a stronghold of Saddam's Sunni Arab minority, where there have been four major military operations since the beginning of May.