By Syed Raza Hassan KARACHI, Pakistan (Reuters) - Gunmen on motorcycles boarded a bus and opened fire on commuters in Pakistan's volatile southern city of Karachi on Wednesday, killing at least 43, police said, in the latest attack directed against religious minorities this year. The pink bus was pockmarked with bullet holes and blood saturated the seats and dripped out of the doors on to the concrete. "As the gunmen climbed on to the bus, one of them shouted, 'Kill them all!' Then they started indiscriminately firing at everyone they saw," a wounded woman told a television channel by phone. Police Superintendent Najib Khan told Reuters there were six gunmen and that all the passengers were Ismailis, a minority Shi'ite Muslim sect. Pakistan is mostly Sunni. Militant group Jundullah, which has attacked Muslim minorities before, claimed responsibility. The group has links with the Pakistani Taliban and pledged allegiance to Isl...