Two people have been killed in an explosion in Przewodow, a village in eastern Poland near the border with Ukraine as NATO allies investigate reports the blast resulted from Russian missiles.
The Associated Press earlier cited a senior United States intelligence official as saying the blast was due to Russian missiles crossing into Poland.
But the Pentagon said it could not confirm that account.
The White House also said it could not confirm reports coming out of Poland and was working with the Polish government to gather more information.
Russia’s defence ministry denied reports Russian missiles had hit Polish territory, describing them as “a deliberate provocation aimed at escalating the situation”.
It added in a statement: “No strikes on targets near the Ukrainian-Polish state border were made by Russian means of destruction.”
The Kremlin did not immediately respond to requests for comment.
Polish Prime Minister Mateusz Morawiecki has called an urgent meeting of a government committee for national security and defence affairs, government spokesman Piotr Muller said on Twitter.
Latvian Deputy Prime Minister Artis Pabriks said on Twitter Russia “fired missiles which target not only Ukrainian civilians but also landed on NATO territory in Poland”.
Officials from Norway, Lithuania and Estonia – members of the NATO defence alliance – said they were trying to find out more.
“This is a very serious incident but much remains unclear,” Norwegian Foreign Minister Anniken Huitfeldt said, according to Norwegian news agency NTB.
Members of the North Atlantic Treaty Organisation (NATO) are committed to collective defence and the possibility the Polish explosion resulted from an intentional or accidental Russian strike raised alarm.
“Every inch of #NATO territory must be defended!,” Lithuanian President Gitanas Nauseda said on Twitter.
Estonian Foreign Minister Urmas Reinsalu said, according to BNS newswire: “We are discussing with our allies how to respond to what happened jointly and decisively.”
Polish Radio ZET reported earlier that two stray missiles hit Przewodow, killing two people, without giving any more details.
“Firefighters are on the spot. It’s not clear what has happened,” said Lukasz Kucy, an officer on duty at a firefighters’ post near the Polish village.
Russia was pounding cities across Ukraine with missiles on Tuesday, in attacks Kyiv said were the heaviest wave of missile strikes in almost nine months of war.
Some hit Lviv, which is less than 80km from the border with Poland.
Muller told reporters later on Tuesday the committee was convened due to the “crisis situation”, adding relevant information would be presented to the public later.
He called on media not to publish “unverified information” in the meantime.