NATO envoys will hold an emergency meeting on November 16 at the request of Poland to discuss reports that two stray Russian missiles aimed at Ukraine landed in the NATO member, killing two people.
The meeting is to be held on the basis of the alliance's Article 4, Reuters reported, citing two unidentified European diplomats. According to Article 4 of the alliance's founding treaty, members can raise any issue of concern when any NATO member feels its "territorial integrity, political independence, or security" are at risk.
"We are verifying the rationale for the use of Article 4," said Jacek Siewiera, head of Poland's National Security Council. "We are in very intensive contacts with key allies."
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Reports on November 15 that two blasts in a village in eastern Poland near the border were caused by Russian missiles that crossed into Poland set off a flurry of calls between the leaders of countries in the alliance.
U.S. national-security adviser Jake Sullivan spoke with Siewiera, White House National Security Council spokeswoman Adrienne Watson said in a statement.
Siewiera later tweeted that Polish President Andrzej Duda spoke by phone to U.S. President Joe Biden, who reaffirmed the "ironclad" U.S. commitment to NATO after the call, the White House said. Biden also offered full U.S. support for assistance with Poland's investigation into the explosions.
The United States and Western allies said earlier they were investigating reports of the explosions but could not confirm them or any details. "We will determine what happened and what the appropriate next steps would be," Watson said in the National Security Council statement.
Poland put its military on heightened alert after an emergency meeting of the country's National Security Council. "There has been a decision to raise the state of readiness of some combat units and other uniformed services," Polish government spokesman Piotr Muller told reporters after the meeting in Warsaw.
Hungary, also a NATO member bordering Ukraine, convened its National Defense Council in response to the reports, a spokesman for Prime Minister Viktor Orban said.
Members of NATO are committed to collective defense enshrined in Article 5 of the alliance's founding treaty, but even if a cross-border strike is confirmed, the response would likely be influenced by whether it was accidental or intentional.
Russia denied its missiles hit Polish territory, saying the reports were "a deliberate provocation" to escalate the situation.
"There were no strikes on targets near the Ukrainian-Polish state border by Russian weapons. The wreckage published by the Polish mass media from the scene of the incident in the settlement of Przewodow has nothing to do with Russian weapons," the Russian Defense Ministry said.
Kremlin spokesman Dmitry Peskov said later he had no information on the explosion in Poland, according to Reuters.
WATCH: Russia launched a barrage of missiles at Ukraine on November 15, hitting energy infrastructure facilities in regions across the country and plunging Kyiv and other cities into darkness.
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Russia Hits Ukraine With Barrage Of Missiles
The missile strikes on NATO territory represented a significant escalation, Ukrainian President Volodymyr Zelenskiy said.
"Today Russian missiles hit Poland, the territory of an allied country. People died," Zelenskiy said in his nightly address to the nation, calling for unspecified action in response.
U.S. State Department deputy spokesman Vedant Patel said the reports coming out of Poland were "incredibly concerning," adding that Washington was working to determine what happened and appropriate next steps.
The State Department is talking to a range of partners about the reports and is working with the Polish government, Patel told reporters at a regular news briefing.
Firefighters quoted by Polish media said two people were killed in an explosion in Przewodow, a village in eastern Poland about 12 kilometers from the border with Ukraine.
Polish Radio ZET attributed the explosion to two stray missiles, without giving more details.
The situation arose as Russia launched a barrage of missiles at sites across Ukraine aimed at crippling the country's energy infrastructure.
Ukrainian officials said more than 90 missiles were fired in the attacks, some of the heaviest attacks since Russia launched its invasion of Ukraine in late February, hitting cities such as Kyiv and Lviv.
With the attacks hitting a NATO member, many countries in the region reacted swiftly, warning the incident could further raise already-high tensions between the West and Moscow.
Estonia's Foreign Ministry called the news from Poland "most concerning" and said that Tallinn would consult with Warsaw and other NATO allies.
Poland's neighbor Lithuania voiced similar sentiments, adding that "every inch of NATO territory must be defended."
"Today's massive missile attacks by the Russian Army on Ukraine clearly show that Russia wants to further terrorize its people and destroy the country," added Czech Prime Minister Petr Fiala on Twitter.
"If Poland confirms that the missiles also hit its territory, this will be a further escalation by Russia," he added.