Czech officials say an explosion of unknown ammunition in an eastern town has killed one man and seriously injured three other people.Rescuers unsuccessfully tried for 45 minutes to save the life of a 34-year-old man who sustained numerous injuries in the explosion on Saturday night in the town of Vitkov, AP quoted Lukas Humpl, a spokesman for the regional rescue service, as saying.In a Sunday statement, Humpl says three other people - men aged 36 and 27, and a 26-year-old woman - were hospitalized in the regional capital of Ostrava in very serious condition.Police spokesman Rene Cernohorsky says the four were handling the ammunition when the explosion occurred.