Poland on Wednesday said that two persons were killed after a “Russian-made” missile fell within its territory in the Przewodow village near the border with Ukraine, reported the Associated Press.

Polish President Andrzej Duda, however, said it was unclear from where the missile had been fired.

“We do not have any conclusive evidence at the moment as to who launched this missile…” Duda said, according to the BBC. “It was most likely a Russian-made missile, but this is all still under investigation at the moment.”

Poland’s Foreign Minister Rau Zbigniew said that he has summoned the Russian ambassador to explain the incident.

Russia has denied any involvement in the incident.

Three United States officials told the Associated Press on the condition of anonymity that preliminary assessments suggested that the missile was fired by Ukrainian forces at an incoming Russian missile. Ukraine still has stocks of Soviet and Russian-made weaponry, including the S-300 air-defence missile system, according to the news agency.

However, US President Joe Biden said that it is unlikely that the missile came from Russia, AFP reported. The Kremlin praised Washington’s “measured response”.

The incident has drawn concern from members of the North Atlantic Treaty Organization, or NATO, of which Poland is a member. The organisation has called for an emergency meeting later on Wednesday to discuss the matter.

Ukraine President Volodymyr Zelenskyy blamed Russia for escalating tensions and said that the strike in Poland was proof that “terror is not limited by our state borders”.

Russia had launched an invasion of Ukraine on February 24. The Kremlin described its actions as a “special operation” to demilitarise and “de-Nazify” Ukraine. However, Kyiv and several Western nations have said that this is a baseless pretext for a war of choice by Russian President Vladimir Putin.

According to the United Nations Human Rights Office, the conflict has killed at least 6,557 persons as of November 14 in Ukraine. On the Russian side, 5,937 soldiers have died, according to the country’s military.

“The longer Russia feels this immunity, the more threats there will be against anyone within reach of Russian missiles,” Zelenskyy said, according to AFP. “Firing missiles at NATO territory is a Russian attack on collective security. This is a very significant escalation. We must act.”

Meanwhile, the Russian defence ministry described media reports on the incident as “a deliberate provocation aimed at escalating the situation”, reported Reuters.

“No strikes on targets near the Ukrainian-Polish state border were made by Russian means of destruction,” the ministry said in a statement.

Unlikely that missile was fired from Russia: Joe Biden

United States President Joe Biden said it was unlikely that the missile responsible for killing two people in a Polish village had been fired from Russia.

Biden said there is “preliminary information that contests” whether the missile was fired from Russia.

“I don’t want to say that until we completely investigate, but it’s unlikely in the minds of the trajectory that it was fired from Russia,” Biden said, according to the BBC. “But we’ll see.”

Biden made the remarks after he held an “emergency roundtable” of G7 countries at the G20 Summit in Indonesia.

The G7 countries, along with NATO, also issued a joint statement offering support to Poland.

“We offer our full support for and assistance with Poland’s ongoing investigation,” the statement said. “We agree to remain in close touch to determine appropriate next steps as the investigation proceeds.”

The G7 consists of Canada, France, Germany, Italy, Japan, the United Kingdom and the United States.