The incident happened on Friday morning, Polish Army's Operational Command said.
Poland's armed forces said on the X social media platform that "in the morning, an unidentified air object flew into Poland's airspace from the direction of the border with Ukraine, and was monitored by the radiolocation devices of the national air defence system."
The object was monitored "from the moment of crossing the border until the place where its signal died down," officials added.
In response to the incident, the Polish Army's Operational Commander "launched the means and forces at his disposal," in line with procedures, the statement added.
On Friday morning, Russia fired drones and missiles on Ukraine in its biggest air attack for months, killing at least twelve people and injuring 60 others, including hitting a critical infrastructure facility in the Lviv region bordering Poland, according to officials in Kyiv.
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Source: IAR, PAP, Polish Army