Polish Prime Minister Donald Tusk announced Wednesday that Poland has formally requested the activation of Article 4 of the North Atlantic Treaty, following reports that Russian drones violated Polish airspace during overnight strikes on Ukraine.

Addressing parliament, Tusk said consultations with allies are “now taking the form of an official request to trigger Article 4 of the NATO Treaty,” signed in 1949.

Article 4 stipulates that member states will consult together whenever one of them perceives a threat, marking a significant diplomatic and security escalation within the alliance amid the ongoing war in Ukraine.