CAIRO (Reuters) - One Egyptian Christian was shot dead on a train on Tuesday and at least three others were injured, medical and security sources said, less than two weeks after a church was bombed in Egypt's deadliest sectarian attack in years. It was not immediately clear if the shooting incident was religiously motivated. Mariam Salah, a doctor at a hospital in southern Egypt, said the institute was treating five injured Christians. She said one of them told her a sixth Christian was shot dead. A security source confirmed one had been shot dead but said three were wounded.