The U.S. military says three coalition soldiers were killed in in southern Iraq after their base was hit by a rocket or mortar attack. The soldiers were attacked at about 9:15 p.m. Thursday. Friday's statement added that an investigation into their deaths is under way. Basra, the country's second largest city, has been peaceful, for the most part, since the Iraqi army mounted a campaign against the militias there in March 2008. Prior to that time, however, British troops in the area were attacked by mortars on a regular basis.