Russian President Vladimir Putin and Belarus strongman Alexander Lukashenko will meet Friday after the UN civil aviation agency announced it will investigate the diversion of a passenger plane and the arrest of a journalist on board in a growing diplomatic row.

The meeting in Sochi between the Kremlin and the Belarusian leader, who enjoys strong support from Moscow, comes as airlines revealed Russia has blocked some European flights for avoiding Belarus airspace.

The G7 global powers have demanded Belarus release the journalist, Roman Protasevich, and the EU's foreign policy chief threatened hard-hitting economic sanctions.

The Montreal-based International Civil Aviation Organization (ICAO) Council said it had "decided to undertake a fact-finding investigation of this event".

It added the body "underlined the importance of establishing the facts of what happened, and of understanding whether there had been any breach by any ICAO Member State of international aviation law."

Lukashenko sparked international outrage by dispatching a fighter jet Sunday to intercept a Ryanair flight from Athens to Vilnius carrying Protasevich, 26, and his girlfriend Sofia Sapega, 23.

A nervous-looking Protasevich was last seen in a video released by Belarusian authorities on Monday in which he was seen supposedly admitting to helping to organise mass unrest, a charge that could land him 15 years in jail.

"I want you to relay our appeal everywhere, throughout the world, to government representatives, to EU countries, to EU leaders, to US leaders: I am appealing, I am begging, help me free my son," his mother Natalia told journalists in Warsaw, visibly moved.

His father Dmitry said his son was "a tough man" and "a hero", adding: "Throughout his life he fought for the truth and passed it on to people, which is why Lukashenko committed this despicable act."

The couple and their lawyer confirmed they have not had any communication with Protasevich since his arrest.

'Immediate and unconditional release'

Foreign ministers of the Group of Seven wealthy nations on Thursday demanded the "immediate and unconditional release" of Protasevich, "as well as all other journalists and political prisoners held in Belarus", in a joint statement published by the British government.

The European Union's foreign policy chief Josep Borrell said proposals were "on the table" to target key sectors of the Belarusian economy.

He mooted targeting the potash fertiliser sector or refusing gas being delivered to the bloc via Belarus over the "hijacking" of the plane by the regime.

Borrell was echoed by German Foreign Minister Heiko Mass, who also raised the possibility of hitting key firms in the fertiliser sector and said the EU could curb the Belarusian government's ability to issue bonds in Europe.

But he played down the likelihood of the bloc agreeing quickly to reject gas transiting through pipelines in Belarus, insisting it was "more of a medium and long-term issue".

The bloc was also looking at "targeted sanctions" against the Belarusian authorities to add to the 88 regime figures and seven companies already on a blacklist over a brutal crackdown on the opposition after last year's disputed presidential election.

At a Thursday briefing in Vilnius, where she fled after last year's election, exiled Belarusian opposition leader Svetlana Tikhanovskaya called for an "economic boycott of the regime".

Christophe Deloire, head of media rights watchdog Reporters Sans Frontieres (Reporters Without Borders) was also in Lithuania to file a legal complaint against Lukashenko with prosecutors investigating Sunday's incident.

Lukashenko still enjoys solid support from Putin, with the Kremlin website describing "integration" between the two nations as "a long-term cherished project for Moscow" ahead of their meeting at the Russian leader's summer residence in Sochi.

Air links cut

The ICAO, of which Belarus is a member, has no power to order sanctions and Russia's support for Minsk means the UN Security Council is unlikely to agree on a collective statement.

However EU nations are banning Belarusian carriers and the EU has also urged airlines to avoid the country's airspace.

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.

'Europe's last dictator'

A defiant Lukashenko said he had "acted lawfully to protect our people" from an alleged bomb threat on the plane, in a parliament address Wednesday.

The criticism was nothing more than another attempt by his opponents to undermine his rule, he added.

Lukashenko -- often dubbed "Europe's last dictator" -- is facing some of the strongest international pressure of his nearly 27 years ruling ex-Soviet Belarus.

He and his allies are already under a series of Western sanctions over a crackdown on protests after his disputed re-election to a sixth term last August.