Article 4 of NATO’s treaty allows a member to formally consult with allies whenever their territorial integrity, political independence or security is threatened.

Article 4, the shortest of the NATO treaty’s 14 articles, states that: “The Parties will consult together whenever, in the opinion of any of them, the territorial integrity, political independence or security of any of the Parties is threatened.”

Estonia’s government said it would request consultations under Article 4 after officials said Saturday that Russian pilots ignored signals from Italian jets responding from NATO's Baltic Air Policing Mission when they violated Estonian airspace.

The 12-minute incursion was the latest test of the alliance's ability to respond to Russian airborne threats after around 20 Russian drones entered Polish airspace on Sept. 10.

AP video shot by Mark Carlson