A bomb placed on a bicycle in a busy market killed four people Sunday, including two children, while American fighter aircraft and ground forces killed 19 militants near the Pakistan border, officials said. The bicycle bomb went off in Gereshk district of southern Helmand province. Doud Ahmadi, spokesman for the provincial governor, said a 10-year-old boy and an 8-year-old girl were among the victims. The Interior Ministry said it exploded in a market while people were shopping. American fighter aircraft and U.S. and Afghan ground forces, meanwhile, killed the 19 militants in a rugged region of eastern Afghanistan along the border with Pakistan, the Associated Press quoted U.S.-led coalition as saying.