A Russian-made missile fell five miles from the Ukrainian border in Przewodów, Poland on Nov. 15, killing two citizens. The cause and origin of the missile are under investigation, and Russia has denied involvement thus far. 

Poland, a member of NATO since 1999, became the first country apart of the alliance to be directly impacted by the Russia-Ukraine War. 

As stipulated in Article 5 of NATO’s founding treaty, should another country provoke any of the organization’s nations, “an armed attack against one or more of the Parties shall be considered an attack against them all.” 

“If such an armed attack occurs,” the Article said, “Each of them will assist the Party or Parties attacked by taking action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.”

Poland held an emergency meeting on Tuesday, though President Andrzej Duda added that Article 4 of NATO’s treaty may be invoked, which would allow Poland to call a meeting with its, “territorial integrity, political independence or security,” threatened.

The tragedy coincides with the Ukraine facing the most intense shelling from Moscow in weeks after Russia’s loss at Kherson. 

“What happened today was what we were warning about for a long time—terror is not confined to our state borders,” Ukrainian President Volodymyr Zelensky said in a video address. “It’s a significant escalation. Action is required.”