Warsaw called emergency meetings of its national security council and cabinet after Russian missiles reportedly had landed in Poland near the Ukrainian border on Tuesday, but the Russian Defense Ministry quickly rejected the claims.
"Due to the crisis situation, Prime Minister Mateusz Morawiecki... called a meeting of the National Security Bureau," government spokesman Piotr Muller told reporters.
There will also be a cabinet meeting, PAP news agency reported, citing the government.
The emergency talks come after a wave of missile strikes across Ukraine on Tuesday which plunged seven million homes into darkness just days after a humiliating Russian retreat.
The strikes also hit Lviv in western Ukraine, with the city's mayor reporting 80% of the city was without power.
Russia rejects reports
Russia's Defense Ministry denied reports that two of its missiles went astray and struck a Polish village near the border with Ukraine on Tuesday.
The ministry called the allegations a "deliberate provocation" to spread false news about Russia, state news agency TASS reported.
No Russian missiles were fired at targets near the Polish-Ukrainian border and images of the alleged wreckage circulating on social media and some news outlets "has no relation to Russian weaponary."
If confirmed, it would be the first such incident in Russia's nearly nine-month war in Ukraine and could mark a dramatic escalation in Moscow's confrontation with the West.
US says 'looking into' reports of Russian missile strikes in Poland
The U.S. Defense Department said Tuesday it was unable to corroborate media reports that two Russian missiles had landed inside NATO member Poland, but added it was investigating the claims.
"We are aware of the press reports alleging that two Russian missiles have struck a location inside Poland or the Ukraine border," said Pentagon spokesman Pat Ryder.
"We have no information right now to corroborate that there has been a missile strike," Ryder told reporters, adding that the Pentagon was "looking into this further."
Poland borders Ukraine, which Russian President Vladimir Putin invaded on Feb. 24, and has welcomed thousands of Ukrainian refugees displaced by the fighting.
Moscow pounded Ukrainian cities with missiles on Tuesday, plunging seven million homes into darkness, and dampening jubilation over the humiliating Russian retreat from Kherson city.
It was not clear if the missiles which may have hit Poland were part of the same wave.
Some 10,000 U.S. personnel are on rotation in Poland, which is a regular contributor to NATO missions, according to official government sources.
Ryder said protecting those troops would be taken "very seriously."
"We're very confident in any force protection measures that we take, whether it be Poland or elsewhere," he said.
"But again, we're not going to get ahead of ourselves here. We're going to get the facts. And then when we have more to provide, we will."
Estonia, Latvia express concern
Estonia and Latvia expressed concern over alleged Russian missiles hitting Poland, a NATO member.
"Latest news from Poland is most concerning. We are consulting closely with Poland and other Allies," the Estonian Foreign Ministry said on Twitter.
"Estonia is ready to defend every inch of NATO territory. We're in full solidarity with our close ally Poland," the ministry added.
Meanwhile, Latvia's Foreign Minister Edgars Rinkevics described the incident as a "dangerous escalation by the Kremlin" in a tweet.
"Russian missiles hitting the territory of the NATO member is a very dangerous escalation by the Kremlin, #Latvia expresses full solidarity with our ally Poland and will support any action deemed appropriate by Poland," said Rinkevics.
"Russia will bear full responsibility for all the consequences," he added.