NATO member states Poland, Estonia, Latvia and Lithuania have triggered NATO Article Four to launch consultations within the alliance over their security concerns.
Estonian Prime Minister Kaja Kallas said Russia’s invasion of Ukraine represented a “threat to the whole of Europe,” the Estonian government said in a statement on Thursday.
"Russia's widespread aggression is a threat to the entire world and to all NATO countries, and NATO consultations on strengthening the security of the Allies must be initiated to implement additional measures for ensuring the defense of NATO Allies,” Kallas said. “The most effective response to Russia's aggression is unity.”
Some context: Under Article 4 of the North Atlantic Treaty Organization (NATO) Agreement, the Parties will consult together whenever, in the opinion of any of them, the territorial integrity, political independence or security of any of the allies is threatened.
Ukraine is not a member of NATO. However, Russia has demanded that NATO commits to never admitting Ukraine to the alliance, something NATO members have rejected, citing the alliance's "open door" policy.