A bomb left over from the Vietnam War years exploded in central Laos, killing two people and injuring another seven, Radio Vientiane reported yesterday. The recent explosion occurred in the Phoukhoun district of Luang Prabang province, said the state-run radio, in a broadcast monitored in Bangkok. The radio called on authorities to step up weeping operations in Luang Prabang to rid the area of unexploded bombs.