"The two Spanish pilots and the two German officers on board the helicopter have died as a result of the accident," the ministry said in a statement. The Spanish BO-105 helicopter "was transporting personnel" when it crashed in the Banja Luka region "for reasons that are not yet known," it said.
The EUFOR helicopter went down in a mountainous, heavily forested area near the town of Travnik at around noon (1000 GMT), shortly after the crew made a Mayday call, it said in a statement.
The helicopter had taken off on a routine flight around half an hour earlier from Camp Butmir in the Bosnian capital Sarajevo.
EUFOR, which took over from a NATO peacekeeping mission in 2004, is charged with military tasks set out in the peace deal that ended Bosnia's 1992-1995 war. It currently has around 2,200 troops in the country.