NATO Secretary General Jens Stoltenberg on Sunday warned Russia and Belarus against threatening the alliance's allies, following the forced landing of a passenger plane within the European Union (EU0 by Belarusian authorities.
"We are of course ready, in an emergency, to protect and defend any ally against any kind of threat coming from Minsk and Moscow," dpa news agency quoted Stoltenberg as saying to the Welt am Sonntag newspaper.
"We are vigilant and we are following what is happening in Belarus very closely," he said.
Belarus is becoming "more and more dependent" on Russia, he added.
Stoltenberg said NATO was seriously concerned about the closer cooperation between Moscow and Minsk in recent months.
"We have had to learn in the past that Russia has massively violated the territorial integrity of states such as Ukraine, Georgia and Moldova."
He did not want to speculate too much, Stoltenberg said, noting, "NATO is a defensive alliance."
Lithuania, Latvia and Poland, all members of NATO, share borders with Belarus.
On May 23, Belarusian President Alexander Lukashenko forced a Ryanair commercial flight between two EU capitals, Athens and Vilnius, to make an emergency landing in Minsk.
Dissident journalist Roman Protasevich and his girlfriend Sofia Sapega, passengers on the plane, were arrested and are being held in custody.
While the EU responded with sanctions on Belarus, Russian President Vladimir Putin hosted Lukashenko for talks and said Moscow would support Belarus with $500 million in credit.
Putin also underlined his continuing support for Lukashenko in his confrontation with the West.