An explosion in Cairo's historic centre on Thursday was caused by a male pedestrian throwing a bomb in the area popular with tourists, Greater Cairo's security director Nabil el-Azabi said. Health and police officials have said the explosion killed up to 4 people, among them a U.S. citizen and a French citizen, and wounded 18 others. Police sources earlier said a man riding a motorcycle had thrown the bomb. Azabi said a parked motorcycle was present in the area of the bomb but was not connected to the explosion. --SP 2249 Local Time 1949 GMT