STORY: As Russian forces launched another wave of missile strikes on Ukrainian cities Tuesday, including the capital Kyiv, in one of the largest salvos of the war.
Reports emerged of an explosion in eastern Poland near the border with Ukraine, killing two people, according firefighters.
NATO said it was investigating reports that the blast resulted from Russian missiles.
If confirmed, it would be the first time Russian aggressions in Ukraine had spilled over the border into NATO territory.
The Pentagon and the White House said – as of Tuesday afternoon- they could not verify the reports.
Pentagon spokesperson Brigadier General Patrick Ryder :
"We are aware of the press reports alleging that two Russian missiles have struck a location inside Poland near the Ukraine border. I can tell you that we don't have any information at this time to corroborate those reports and are looking into this further,"
Poland is a member of the U.S.-led military alliance NATO, which is committed to collective defense, and the possibility that the Polish explosion resulted from an intentional or accidental Russian strike raised alarm.
U.S. State Department Spokesperson Vedant Patel said The U.S. was talking to a range of partners, and called the reports ‘concerning’.
“We're working with our partners in the Polish government and our NATO partners to get more information and to assess what has happened. We will make that determination and we will determine appropriate next steps as well.”
But Russia's defense ministry denied reports that its missiles hit Polish territory, describing them as "a deliberate provocation aimed at escalating the situation."
Nevertheless, Ukrainian President Volodymyr Zelenskiy on Tuesday blamed Russia, and said it was a "significant escalation" of the conflict.
"The longer Russia feels impunity, the more threats there will be to anyone within reach of Russian missiles. To fire missiles at NATO territory! This is a Russian missile attack on collective security! This is a very significant escalation. We must act."
The explosion in Poland occurred as Russia hammered cities across Ukraine with missiles on Tuesday, attacks that Kyiv said were the heaviest wave of strikes nearly nine months into the Russian invasion. Some hit the western city of Lviv, less than 50 miles from the border with Poland.
The attacks left millions of Ukrainians without energy... including In Kharkiv, where the streets Tuesday were drenched in darkness.