MAZAR-I-SHARIF, Afghanistan - A bicycle bomb killed four civilians and injured eight others on Wednesday in the northern Afghan city of Mazar-i-Sharif, one of seven areas where security control is being handed from foreign to Afghan forces this week, a police spokesman said."We are investigating whether the explosive was attached to his body or his bicycle," said Sherjan Durani, spokesman for the police chief of northern Balkh province, where Mazar-i-Sharif city is located.Two of the injured were children, Durani added.