The 73-year-old military alliance will hold an emergency meeting of its ambassadors on Wednesday to discuss the latest developments after Polish officials emerged from a crisis meeting to say that it was a Russian missile that fell on a village about 6 kilometers (4 miles) from the frontier, killing two people.
Any step by the military alliance would require careful verification of the facts and balance a collective desire not to escalate tensions. Polish President Andrzej Duda struck a note of caution by saying it was unclear who had launched the rocket.
The options range from the expected — a formal discussion with allies, to something no one is even suggesting — invoking Article 5, which was done only once, with the Sept. 11, 2001 terrorist attacks.
What is Article 4?
Under Article 4, NATO members can raise any issue of concern related to territorial integrity, political independence or national security to be discussed among representatives of the member states prior to taking any action.
Latvian Defense Minister Artis Pabriks told Bloomberg TV his country would support Poland in this step, adding the alliance needs to have a serious discussion about its air-defense systems. Indeed, this seems to be where Poland is headed.
Once Article 4 is invoked and the issue is discussed among allies, it can potentially lead to a joint decision or action on behalf of NATO. This step has happened a number of times in the alliance’s history, most commonly stemming from requests made by Turkey. In 2012, NATO granted Turkey’s request to deploy Patriot missiles following meetings with allies under Article 4 to discuss Syrian military activity at its border. The last time Article 4 was invoked was in February by a group of eastern member states after Russian invaded Ukraine.
What is Article 5?
Article 5 is the cornerstone of the alliance and enshrines NATO’s principle of collective defense — that an attack on one member is an attack on all. It has to be raised by a member state claiming they are under direct attack, an assessment that then would need to be unanimously agreed by all allies in order to invoke Article 5.
Once invoked, all members assist the ally attacked, including with armed forces.
To be clear, since its formation in the aftermath of World War II, this last-resort tool has been used only once: 21 years ago, when NATO issued a statement that the US would have the support of NATO allies if it took military action against those it held responsible for attacks on the World Trade Center and the Pentagon.