A deadly explosion occurred in NATO member Poland's territory near its border with Ukraine on Tuesday, and the United States and its allies said they were investigating unconfirmed reports the blast was caused by stray Russian missiles.
The explosion, which firefighters said killed two people, raised concerns of Russia's war in Ukraine becoming a wider conflict. Polish authorities said it was caused by a Russian-made rocket, but Russia's defense ministry denied involvement.
If it is determined that Moscow was to blame for the blast, it could trigger NATO’s principle of collective defense known as Article 5, in which an attack on one of the Western alliance’s members is deemed an attack on all, starting deliberations on a potential military response.