Poland holds emergency security meeting after reports of fatal explosion, as Russian missiles bombard nearby Ukraine

(CNN) -- Poland convened an emergency meeting of national security officials on Tuesday, after Polish media reported projectiles killed two people near the border with Ukraine on Tuesday.

It is unclear where the projectiles came from, but they landed in the NATO member's territory roughly the same time as Russia launched its biggest wave of missile attacks on Ukrainian cities in more than a month.

Polish media showed an image of a deep impact and upturned farm vehicle at the site, near the town of Przewodow, around four miles west from the Ukrainian border.

Polish Prime Minister Mateusz Morawiecki has convened the Committee of the Council of Ministers for National Security and Defense Affairs, a government spokesman said.

A Polish official told CNN that nothing was confirmed yet and the investigation into the incident was continuing.

Russia's Defense Ministry has denied targeting the border, and called the reports by Polish media "a deliberate provocation in order to escalate the situation," according to a short statement late Tuesday.

"The statements of the Polish media and officials about the alleged fall of 'Russian' missiles in the area of ​​the settlement of Przewodow is a deliberate provocation in order to escalate the situation," it said, adding that "there were no strikes made on targets near the Ukrainian-Polish state border."

It added that the photos of wreckage published by the Polish media "from the scene in the village of Przewodow have nothing to do with Russian weapons."

Nevertheless, Ukrainian President Volodymyr Zelensky blamed Russia, describing the fatal explosion as a "significant escalation" in Moscow's invasion.

NATO allies respond

Little is publicly known about the origin of the projectiles.

A NATO official told CNN that it was still waiting to learn more about what happened and are waiting on details from Warsaw.

NATO allies responded with concern to the reports. Some were were circumspect in their statements, neither speculating or confirming the origin of the projectile.

A senior White House official says they do not have confirmation of any rocket or missile strike in Poland, but that US officials are currently working to try and figure out exactly what has happened.

State Department principal deputy spokesperson Vedant Patel echoed that the US cannot confirm the reports of missiles hitting Polish territory and killing two.

"We have seen these reports out of Poland and are working with the Polish government and our NATO partners to gather more information," Patel said at a press briefing. "We can't confirm the reports or any of the details at this time"

A UK Foreign Office spokesperson said they were "investigating these reports and liaising closely with Allies."

Baltic NATO states were more strident in their statements, stressing readiness to defend NATO territory.

Estonia called the news "most concerning," according to a Twitter post from the Estonian Ministry of Foreign Affairs.

"Estonia is ready to defend every inch of NATO territory," it added.

Lithuanian President Gitanas Nauseda has said he was concerned by the news, and that "Lithuania stands in strong solidarity with Poland."

"Every inch of NATO territory must be defended!" he added on social media.

Latvian Defense Minister Artis Pabriks afforded blame on Russia, even though there has been no confirmation from Polish authorities that Russian missiles landed on Polish territory.

"Condolences to our Polish brothers in arms. Criminal Russian regime fired missiles which target not only Ukrainian civilians but also landed on NATO territory in Poland. Latvia fully stands with Polish friends and condemns this crime," Pabriks wrote.

The North Atlantic Treaty Organization is a group of 30 North American and European nations. According to NATO, its purpose "is to guarantee the freedom and security of its members through political and military means."

The alliance was created in 1949 in response to the start of the Cold War. Its original purpose was to protect the West from the threat posed by the Soviet Union. Since the end of the Cold War, many former Soviet nations have joined NATO, much to the annoyance of Putin.

The best-known aspect of the alliance is Article 5 of the treaty, which, if invoked, means "an attack against one Ally is considered as an attack against all Allies."

Article 5 has only ever been invoked once, in response to the September 11, 2001 terrorist attacks on the United States.

However, the alliance can take collective defense measures without invoking Article 5 -- and has done this in the light of the Russian attack on Ukraine.

The State Department's Patel repeatedly said on Tuesday he would not discuss hypotheticals when asked about NATO Articles 4 and 5, but said that intent "is something that would be of importance" in determining a response.

"As I said, we will determine what happened and we will determine appropriate next steps but like I said, this just happened within the past hour and so we are still taking the important time to figure out the exact facts," he said.

Russian President Vladimir Putin has long complained that NATO has, over time, expanded its borders by admitting Eastern European countries that were once part of the Soviet Union -- meaning Russia now shares a land border with the world's largest military alliance, thus reducing his geopolitical power in what was once Moscow's sphere of influence.

As recently as February, he was demanding that NATO scaled back to the borders of 1997, before the Baltic nations of Latvia, Lithuania and Estonia, the latter two of which border Russia, joined the alliance.

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