Serbia's ambassador to NATO jumped to his death from a car park at Brussels airport, officials said on Wednesday.
Branislav Milinkovic, 52, jumped to his death during a conference of NATO foreign ministers, but officials did not make any connection between the meeting and his suicide.
"We are shocked and we are investigating all circumstances" surrounding the ambassador's death, said a Serbian Foreign Ministry official who asked not to be named.
"We have no clues about what could prompt Milinkovic to do that. He was a good man," the official said.
NATO Secretary-General Anders Fogh Rasmussen was "deeply saddened by the tragic death of the Serbian ambassador," who was highly respected, said an alliance spokeswoman.
Brussels prosecutor's office said: "We can be sure that it was a suicide, therefore we are not investigating any further."
The Serbian Foreign Ministry praised Milinkovic as a distinguished diplomat and jurist who would be "remembered as a skilled diplomat, an intellectual and a noble man."
Milinkovic was appointed ambassador to NATO in 2009 but had already been based in Brussels since 2004 as an envoy from the now defunct state union of Serbia and Montenegro.
Serbian tabloid newspaper Kurir reported that Milinkovic jumped around 10 meters (32 feet) in the presence of Serbia's assistant foreign minister for security policy, Zoran Vujic.
The report, which could not immediately be confirmed, quoted an unnamed foreign ministry source as saying: "It's possible the man was depressed and that nobody had noticed."