Two Spanish pilots and two German officers of the European Union's peacekeeping force were killed when their helicopter crashed in central Bosnia on Thursday, authorities said.
The helicopter crashed near the northern town of Kotor Varos in a mountainous, heavily forested and inaccessible area.
"The helicopter was from our Spanish contingent There were no survivors," EUFOR Commander, Major General Ignatio Martin Villalain, said in a statement expressing "deepest sadness".
The cause of the crash of the BO-105 helicopter is being investigated, the statement said.
Local agencies reported that EUFOR had sealed off the area and did not allow anyone near the site.
The EU's 2,000-strong multinational force took over in 2005 from NATO, which had originally deployed at the end of the 1992-95 war. Spain is the biggest contributor to EUFOR.
In a similar incident in September 1997, 12 people including United Nations diplomats were killed in a helicopter crash in central Bosnia.
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