A roadside bomb exploded near a prison van and a school bus in northwestern Pakistan on Thursday, killing at least ten people, a local mayor and a police official said. Three school children, four policemen and three prisoners died in the remote-controlled blast in the Upper Dir district, near the troubled Swat Valley, where troops are battling Islamist militants, they said. "The van was carrying prisoners to jail after court proceedings when the roadside remote-controlled bomb went off," local mayor Sahibzada Tariqullah said, confirming the deaths of the policemen and the prisoners.