"Unfortunately, all five members of the IAR 330 crew lost their lives. Search and rescue operations for the pilot of the MiG 21 LanceR are still ongoing," General Constantin Spanu, spokesman of the Ministry of National Defense, said.

The IAR 330-Puma helicopter crashed in the area of Gura Dobrogei, 11 kilometres (seven miles) from the airfield.

It was searching for the fighter jet, shortly after the jet lost its radio connection with the control tower and disappeared from the radar.

The pilot had reported adverse weather conditions and had been ordered to return to base, Spanu said.

"It is premature to discuss possible causes. Certainly, there were unfavourable weather conditions, but we can't comment now," he told Digi24 television.

"We have two commissions of inquiry set up. Our focus is on the search-and-rescue operation," he said.