A car bomb exploded in downtown Baghdad as a police convoy drove by, police said. "There are definitely casualties," said policeman Medhafar Ismail. He had no details. A witness said shrapnel rained down on his stationary shop in the central Al-Mutanabbi Street. "People coming from the blast location said that a car, a Chevrolet type, exploded," said Haqqi Ismael, 25. "Iraqi police and American soldiers are there now." Security forces blocked off the area. A second blast shook the city less than an hour later. The cause of that explosion was not immediately known. U.S. military and Iraqi Interior Ministry officials had no immediate information on either incident.