Poland has triggered Article 4 of the North Atlantic Treaty Organization, NATO, after the country reported 19 “breaches” of its airspace by Russian drones on Wednesday.

The United States told the United Nations Security Council on Friday it would "defend every inch of NATO territory" after a suspected Russian drone incursion into Poland.

NATO Secretary-General Mark Rutte called Russia's behavior "reckless" after several drones from the country crossed into Poland, violating NATO airspace.

Article 4 allows member states to start a formal discussion within the alliance about threats to their security. It does not commit the alliance to military action.

NATO announced plans to beef up the defence of Europe's eastern flank on Friday, two days after Poland shot down drones that had violated its airspace in the first known action of its kind by a member of the Western alliance during Russia's war in Ukraine.

The Polish prime minister said there had been a serious violation of his country's airspace by Russian drones.

Multiple Russian drones crossed into Poland in what European officials described as a deliberate provocation, causing NATO to send fighter jets to shoot them down.

The incident represented the most serious spillover of the war in Ukraine for NATO, as its aircraft engaged the drones that it said came from Russia.

Lithuania is "ready" to shoot down any more drones that enter its airspace, the country's defense minister told ABC News.

A continent already on edge over the Ukraine war sees a Russian challenge to NATO readiness and to an America that wants to disengage from Europe.

Russian President Vladimir Putin’s main target in the drone incursion into Poland was not necessarily the civilian home that was hit in the eastern town of Wyryki, or to close airspace around the capital Warsaw’s busiest airport.

Poland shot down Russian drones that violated its airspace during a massive strike on Ukraine, prompting NATO consultations, and coordinated defence operations.