The U.S. military said on Monday air strikes had killed about 37 insurgents in the latest phase of an operation near the Syrian border in western Iraq and 25 insurgents had been captured. Operation Steel Curtain, launched just over a week ago, entered a new phase on Monday, the U.S. military said, when U.S. and Iraqi troops moved into the town of Ubaydi, on the banks of the Euphrates river, 20 km (13 miles) from the border. "Five targets were struck by coalition air strikes resulting in an estimated 37 insurgents killed," a statement said. "The insurgents were engaging coalition forces with small arms fire at the time of the strikes. "Insurgent fighters have been battling with Iraqi and coalition forces since the operation began at dawn," it said. About 2,500 U.S. troops and 1,000 Iraqi soldiers have already swept through the towns of Qusayba and Karabila, clearing houses and battling with insurgents, in what the military says is an offensive aimed at rooting out foreign fighters, the Associated Press reported. The operation is also aimed at making it safe for residents to vote in Dec. 15 elections, the military says.