(Adds details) BAGHDAD, June 11 (Reuters) - A suicide car bomb attack on a bridge overpass south of Baghdad late on Sunday killed three U.S. soldiers and wounded six more, U.S. military spokesman Lieutenant-Colonel Randy Martin said on Monday. The soldiers, who had been manning a checkpoint, were killed when part of the span collapsed. "I believe there were folks that were on or near the bridge span that collapsed. Folks were dug out of portions of the bridge that collapsed," Martin said. An Iraqi interpreter was also wounded in the attack which hit near Mahmudiya, 30 km (20 miles) south of Baghdad, in an area notorious for attacks by insurgents linked to al Qaeda. Engineers with heavy machinery were being sent to clear the highway, which was partly blocked by debris, the U.S. military said in a statement. Mahmudiya is in a Sunni Arab stronghold known as "the triangle of death". Two U.S. soldiers have been missing since their patrol was ambushed near Mahmudiya on May 12. Four other U.S. soldiers and an Iraqi interpreter were killed in the attack, responsibility for which was claimed by al Qaeda-led Islamic State in Iraq. A third U.S. soldier was abducted but his body was found almost two weeks later. Thousands of extra U.S. troops are still searching for the missing soldiers. Thousands more have been deployed in Baghdad and other areas as part of a four-month-old security crackdown seen as a last-ditch attempt to avert all-out sectarian civil war between majority Shi'ites and Sunnis dominant under Saddam Hussein. Their increased presence in the capital has forced insurgents out of the capital into outlying cities and towns. A total of 3,511 U.S. soldiers have died since the invasion to topple Saddam began in March 2003. Of those, 127 were killed in May, the third-highest monthly total of the war and the most in one month for two-and-a-half years. Another 34 have died so far in June.
