An explosion at a military plant in central Bulgaria killed one American citizen and injured four other people on Saturday, the US embassy in Sofia said.
Bulgaria's Interior Ministry said earlier in the day that the accident occurred during an experimental production test at a shooting range located in a military complex in the village of Anevo -- part of the state-owned arms producer VMZ Sopot.
"The US Embassy regretfully confirms the death of one Department of Defence contractor and the injury of two other contractors and a Bulgarian translator in a training accident on June 6 in Anevo," the embassy said in a statement.
Bulgarian authorities are investigating the cause of the accident. The US embassy said it did not have any further details.
A series of powerful blasts at an explosives plant in northwestern Bulgaria killed 15 employees and injured three others last October, just two months after government officials warned of serious safety breaches at the factory.