The United States "will defend every inch of NATO territory," Pentagon said after the reports of 2 Russian missiles striking Poland.
Pentagon also said that it is looking into reports of strikes and working to corroborate them.
"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.
"I don't want to speculate or get into hypotheticals. When it comes to our security commitments, and Article Five, we've been crystal clear that we will defend every inch of NATO territory," he added, referring to NATO's collective defense principle.
The reported attacks that hit Poland's eastern village of Przewodow come as Ukraine faces a wave of missile strikes that have again targeted the war-torn country's energy infrastructure, knocking power out for millions of people. Some Russian strikes hit targets in the western part of the country close to the border with Poland.
Polish Prime Minister Mateusz Morawiecki has convened an urgent high-level meeting to discuss the matter, government spokesman Piotr Muller said shortly after reports of the explosion began.
The White House said it is working with Morawiecki's government "to gather more information" on the explosions, and "will determine what happened and what the appropriate next steps would be."
"We cannot confirm the reports or any of the details at this time," National Security Council spokeswoman Adrienne Watson said on Twitter.
Earlier, The Associated Press quoted an anonymous senior American official as saying Russian missiles crossed into NATO member Poland, killing two people.
Russia's Defense Ministry denied carrying out any attacks near the Ukrainian-Polish border.
"The fragments published in hot pursuit by the Polish media from the scene in the village of Przewoduv have nothing to do with Russian weapons," Russia said.
