Poland said early on Wednesday that a missile believed to have been Russian-made fell in the eastern part of the country near the border with Ukraine, killing two people in the blast.
The development marks the first time Russian weapons came down on a NATO country since the invasion of Ukraine.
While Ukrainian President Volodymr Zelenskyy has decried the strike as "a very significant escalation" of the war, Moscow's defence minister on Tuesday dismissed the reports as a "provocation" intended to soar tensions.
Polish Prime Minister Mateusz Morawiecki said the government has raised its military preparedness and is investigating into the incident.
NATO Secretary-General Jens Stoltenberg called an emergency meeting of the alliance's envoys to discuss the events close to the Ukrainian border in Poland.
US President Joe Biden convened an "emergency" meeting of the Group of Seven and NATO leaders in Indonesia on Wednesday morning for consultations on the attack.
He however said that it was "unlikely" that a missile that killed two in NATO-ally Poland was fired from Russia, but pledged support for Poland's investigation.
According to media reports, Russia on Tuesday pounded Ukraine's energy facilities with a barrage of missiles, striking power targets across the country and causing widespread blackouts.
(With Agency Inputs)