The find was made during an investigation into the cause of a blast at a house in the mid-Wales town on Monday night in which a man died and another was seriously injured.
A number of 8oz sticks of PE4 explosives were later recovered from the home of the injured man, a mile from the scene of the blast which police said was caused by 1lb of material.
Richard Livsey, MP for Brecon and Radnorshire, said: "I am contacting the MoD demanding that it checks all procedures for the storage of explosives and the way it accounts for the use of these materials. An MoD spokesman said: "We will help the police in any way we can."Reuse content