EU foreign policy chief Josep Borrell said on Friday that the bloc was monitoring whether Russia was systematically refusing to let European airlines land if they avoided Belarus after several flights were cancelled. 

On Thursday, Austrian Airlines said it had cancelled a Vienna-Moscow flight after Russian authorities did not approve a route change avoiding Belarusian airspace.

An Air France flight from Paris to Moscow on Wednesday had to be cancelled for the same reason.

"We don't know if it is case by case, specific cases, or is a general norm from the Russian authorities in order to make the European planes overfly Belarus," Borrell told journalists. 

"There were a couple of cases. Some planes that couldn't land, couldn't take off. But frankly speaking, we have to wait and see in order to take measures."

Austria denounced Russia, the key backer of Belarusian President Alexander Lukashenko, after it refused to allow the Austrian Airlines flight to be rerouted.

Belarus sparked global fury by diverting an Athens-to-Vilnius Ryanair plane on Sunday and arresting an exiled dissident and his girlfriend who were onboard.

In response, EU leaders on Monday decided to ban Belarusian carriers from European airspace and airports and recommended that EU carriers should also avoid Belarusian airspace.

Austrian Airlines is part of Germany's Lufthansa group.

Lufthansa confirmed to AFP on Thursday that all its airlines were "currently avoiding Belarusian airspace".

Scheduled flights to Moscow and Saint Petersburg continued, it said.