Meanwhile, Air France cancelled more flights to Moscow after Russian authorities failed to approve flight plans that avoid Belarus airspace.
The diversion of a Ryanair flight by Belarus last week was an act of "state piracy," EU commissioner Thierry Breton has said after meeting some of the passengers in Lithuania.
"It is an unacceptable event. There has been a hijack, not just of an EU plane with European passengers, but a hijack of European values and that we will not tolerate," he told AFP on Monday.
The Athens to Vilnius flight on May 23 was forced to land in Minsk and dissident journalist Roman Protasevich and his girlfriend Sofia Sapega were arrested, causing a global outcry.
Europe "has been under attack with this act of state piracy. We will not leave this unpunished," Breton said, adding that the EU was working on additional economic sanctions on Belarus.
Exiled Belarusian opposition leader Svetlana Tikhanovskaya during a visit to Estonia on Monday discussed possible EU economic sanctions with Estonian President Kersti Kaljulaid.
Belarusian President Alexander "Lukashenko has brought Belarus on a path to self-destruction for the sake of personal power and glory," she said at a joint press conference with Kaljulaid.
NATO restricts Belarus personnel access at HQ
Personnel at Belarus' diplomatic mission to NATO will have restricted access to the alliance's headquarters following the forced landing of a passenger plane by Minsk, Secretary General Jens Stoltenberg said.
"We have decided to restrict the access of Belarusian personnel to the NATO headquarters," Stoltenberg told a news conference, without giving more details. NATO and Belarus have had ties since 1992 and the country has had a diplomatic mission to NATO since April 1998.
Asked about new Russian military formations and units, intended to be deployed close to the alliance's borders, Stoltenberg said NATO would continue to seek dialogue with Moscow, while also exercising troops for defensive purposes.
Air France cancels more Moscow flights
Meanwhile, Air France cancelled two more flights to Moscow after Russian authorities failed to approve flight plans that avoid Belarus airspace.
"Air France confirms the cancellation of flights AF1154 and AF1654 from Paris-Charles de Gaulle to Moscow on 31 May 2021 as the authorisations from Russian authorities to enter their territory have not been granted," the airline said.
The French airline, part of the broader Air France-KLM group, was forced to cancel two Paris-Moscow flights last week after receiving no Russian clearance for flight plans skirting the territory.
Obstacles to rerouted Air France flights appeared to have been resolved late last week, allowing Air France to carry out two weekend Paris-Moscow services.
But the latest setbacks occurred after Air France resubmitted routes avoiding Belarus for approval as part of a seasonal renewal process, an Air France spokesperson said.
Russia's federal aviation agency Rosaviatsiya declined to comment on Monday.