(Adds details) BAGHDAD, April 12 (Reuters) - An explosion on a bridge in Baghdad on Thursday killed six people and sent some cars plunging into the Tigris River below, police said. They said the blast had partially destroyed the Sarafiya bridge. The death toll could rise, police said. The Tigris River cuts Baghdad in half and numerous bridges connect each side of the city. U.S. and Iraqi forces launched a security crackdown in the capital two months ago that has managed to reduce sectarian death squad killings, but car bombs have remained a problem.
