BAGHDAD, Iraq (CNN) -- The U.S. military said 20 insurgents were killed and another was captured during raids by coalition forces on "foreign safe houses" Saturday in the western Iraqi town of Husayba.The insurgents were "suspected of sheltering al Qaeda in Iraq" militants, according to a military statement. The raids were staged in a section of Anbar province near the Syrian border. Two neighborhoods were raided, the military said, and coalition forces found "two large weapons caches containing small arms, ammunition, rocket-propelled grenades, mortar rounds, explosives, and bomb-making materials to include radios and detonators."Upon leaving the area, coalition forces used "precision-guided munitions" to destroy a car bomb, five safe houses and weapons caches, the military said.U.S. and Iraqi troops have been launching raids and offensives for months against insurgents in the province.About 60 miles north of Baghdad, in Ad Duluiya, a Task Force Liberty patrol killed an insurgent during a firefight. Another insurgent was wounded and a third was captured.Early vote figures emergeVoters in Diyala province -- a key Iraqi swing province with a significant Sunni Arab presence -- are backing the country's draft constitution, according to unofficial returns from last weekend's referendum.Meanwhile, at least one Sunni-dominated province has emerged overwhelmingly anti-constitution. In Salaheddin province, the home of former dictator Saddam Hussein, 81 percent of the voters cast "no" ballots and 18 percent voted yes.Figures for two other provinces with significant Sunni Arab populations -- Anbar and Nineveh -- were not issued. Should those provinces also turn up "no" votes that surpass two-thirds, the measure will fail.Nearly 10 million people voted in the referendum.Fareed Ayar, spokesman for the Independent Electoral Commission of Iraq, told CNN that the numbers released on Saturday represent about 34 percent of those who voted in the referendum. (See breakdown by province so far)U.S. troops killedThe military announced Saturday the deaths of four U.S. troops in Iraq this week, bringing the total U.S. death toll in the war to 1,993.Two Marines were killed Friday in a roadside bombing near Amariya in Anbar province.Both were assigned to Regimental Combat Team 8, 2nd Marine Division, II Marine Expeditionary Force (Forward).A third Marine was killed by an explosion Friday in the vicinity of Haqlaniya. "During the subsequent engagement, Marines killed four insurgents and destroyed a bunker adjacent to their position with an unknown number of insurgents firing from inside," the military said in a news release. The dead Marine was assigned to Regimental Combat Team 2, 2nd Marine Division, II Marine Expeditionary Force (Forward).Also, a Task Force Baghdad soldier was killed Thursday from a "non-hostile gunshot wound" in central Baghdad, the military said.