Poland is a member of NATO, and the killing of two of its civilians could bring the country and the entire alliance into direct conflict with Russia.
A Russian missile killed two people in Przewodow, a Polish village near the border with Ukraine, on Tuesday, according to reports.
The strike was part of Russia's missile barrage that targeted at least seven cities across Ukraine, marking the end of a lull in such attacks that had slowed since the start of November. Western parts of Ukraine have largely been shielded from the direct battleground, though the area has remained within striking distance of Russia's aerial arsenal.