The IAR 330-Puma helicopter crashed in the area of Gura Dobrogei, 11 kilometres (seven miles) from the airfield, killing all seven people aboard, according to the ministry of defence.

It was searching for a MiG 21 LanceR, shortly after the fighter jet lost radio contact with the control tower during an air patrol mission and disappeared from the radar.

"Search and rescue operations for the pilot of the MiG 21 LanceR aircraft are still ongoing," a statement from the defence ministry said.

Authorities are still investigating the cause of the helicopter crash.

The helicopter pilot had reported adverse weather conditions and had been ordered to return to base, according to the ministry.

"It is premature to discuss possible causes. Certainly, there were unfavourable weather conditions, but we can't comment now," spokesman General Constantin Spanu said on local television.

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

- 'Tragic night' -

President Klaus Iohannis in a statement sent his "thoughts to the bereaved families" of the crash victims on what he called "a tragic night for Romanian aviation".

In July 2020, 12 people were killed and two injured when an AN-2 aircraft crashed on a parachute training flight mission, shortly after take-off.

This led Romania's army to give up the aircraft type, no longer considered safe.

Later that month, six Israeli soldiers and a Romanian died when their helicopter crashed in central Romania.

Crashes of the MiG 21 LanceR occur occasionally.

In 2018, a Romanian Air Force pilot died after his MiG 21 LanceR crashed during an air show in the southeast of the country.

The Romanian Air Force still relies on the Soviet-era MiGs for missions of air policing, though it is modernising its aircraft.

- NATO's eastern flank -

Romania, a former member of the communist bloc now part of NATO and the European Union, borders Ukraine and has seen tens of thousands of refugees arrive since Russia invaded its neighbour last week.

Over the past months of growing regional tensions, Romania has repeatedly demanded reinforcements be sent to NATO's eastern flank.

Its allies have responded.

The United States has sent a squadron of Stryker armoured vehicles and some 1,000 troops in recent weeks to a Romanian base near the Black Sea, adding to the 900 personnel already stationed in the country.

And over the past month, six Eurofighter Typhoon aircraft from Germany's air force have joined four similar planes Italy dispatched before the crisis.

More than 500 French soldiers are being sent to the eastern European country this week.

The situation has been complicated by Russia's seizure from Ukraine on Thursday of Snake Island, an uninhabited but strategic rocky outcrop in the Black Sea just 45 km (27 miles) from Romania's coast.

Bucharest and Kyiv both claimed the island, before the International Court of Justice awarded it to Ukraine in 2009.