US President Joe Biden ruled out that the missile, which fell in Poland, was launched from Russian territory.
Polish officials said the missile was “Russian-made”, noting that it killed two people in a region on the border with Ukraine.
But Moscow confirmed that it did not carry out any missile strikes near the Polish-Ukrainian border.
The Russian Defense Ministry said in a statement that the reports about Moscow’s involvement in the incident were a “provocation” with the aim of escalation.
Biden met with the leaders of a number of countries, on the sidelines of the G20 summit in Indonesia, in “emergency” talks to discuss developments in Poland.
Among those present were President Biden, British Prime Minister Rishi Sunak, French President Emmanuel Macron and European Commission President Ursula von der Leyen.
The US president said, in remarks early Wednesday morning, that “preliminary information” contradicts reports about Russia’s involvement in the incident.
Reports of a missile hitting Poland, a NATO member, came after Russia launched a new wave of attacks across Ukraine on Tuesday.
Russia denied the allegations of responsibility for the incident, which took place in Poland, and the Ministry of Defense in Moscow attacked what it called a “deliberate provocation aimed at escalating the situation.”
Kremlin spokesman Dmitry Peskov also said he had no information about the explosion.
The Russian state news agency, RIA Novosti, said that Ukrainian missiles hit Polish territory.
But Ukrainian Foreign Minister Dmytro Kuleba said any claim that Ukraine was responsible was a Russian “conspiracy theory”.
Polish President Andrzej Duda told reporters it was still not clear how the accident happened, and said investigators were evaluating all possibilities.
“We don’t have any conclusive evidence at the moment as to who fired this missile,” he said. “The missile was most likely Russian-made, but all of this is still under investigation at the moment.”
A spokesman for Poland’s Foreign Ministry, Lukasz Jasina, announced that the Russian ambassador had been summoned to request “immediately detailed clarifications” about the incident.
The Polish National Security Council also held an emergency session.
And if a missile is confirmed to have landed in the area, it will be the first time a missile has landed on the territory of a NATO member since the start of Russia’s invasion of Ukraine in February.
Polish government spokesman Piotr Mueller confirmed that Warsaw is raising the alert of military units and “checking whether we need to activate NATO’s Article 4”.
According to this article, “the parties shall consult when either of them deems a threat to the territorial integrity, political independence, or security of any of the parties.”
NATO Secretary General Jens Stoltenberg said in a tweet that he spoke to the Polish president after the incident.
“I offered my condolences for the loss of life. NATO is monitoring the situation and consulting allies closely. It is important that all facts are established,” he said.
And despite providing support to Ukraine since the Russian invasion, NATO has been careful not to get too involved in the conflict in order to prevent escalation.
The G7 issued a statement condemning Russia’s “barbaric missile attacks” on Tuesday, and addressing the “explosion”.
“We offer our full support and assistance in the ongoing investigation. We agree to remain in close contact to determine appropriate next steps as the investigation continues,” she said.
Meanwhile, UN Secretary-General Antonio Guterres said he was “deeply concerned” by Poland’s implosion and called for a thorough investigation.
“It is absolutely necessary to avoid an escalation of the war in Ukraine,” said his spokesman, Farhan Haq.
The BBC’s Paul Adams says there are a number of possible explanations for the accident.
He noted that Russia has no interest in targeting Polish farms, so it seems likely that something will go wrong.
Adams added that on a day when Ukrainian air defenses were working hard to shoot down Russian missiles, it is also possible that one of those missiles went off course.
The attacks came after one of the heaviest days of Russian forces bombing Ukraine since the start of the war.
Ukraine was hit by more than 90 missiles on Tuesday, according to Ukrainian Air Force spokesman Yuriy Ikhnato, who said more than 70 missiles were successfully shot down.
Ukrainian President Volodymyr Zelensky said most of the missiles launched were aimed at the country’s energy infrastructure.
Zelensky accused Russia of deliberately attacking Poland.
“This is a Russian missile attack on collective security. This is a very significant escalation. We must act,” he said.
“Terrorism is not confined to our national borders,” he said, adding that it was “only a matter of time before Russian terrorism goes further.”
Zelensky said, and his country is not a member of NATO but has close relations with the alliance, that the missile attack on the electricity network in his country was “a slap in the face of the Group of Twenty.”
“Committing the genocide of Ukrainians in response to my peace plan is a cynical slap in the face to the G20 and the world,” he wrote on Telegram.
Belgian Prime Minister Alexander De Cree said that his country stands by Poland and that the NATO family is more united than ever.
Lithuanian President Gitanas Nauseda said every inch of NATO’s territory must be defended.
And in Slovakia, Defense Minister Jaroslav Nad said Russia should explain what happened.
Social media photos show damage believed to be caused by a missile, in addition to parts of it, as it is believed.
The BBC has not been able to verify the authenticity of the photos, but has spoken to three defense experts about what they contain.
Mark Cancian, of the CSIS Research Center, believes that it may be the remnants of a missile from the S-300 system. This type of missile is usually used in launching surface-to-air attacks, and Russia and Ukraine have used it throughout the war.
“It’s not clear the missile was fired,” said J. Andres Gannon, a security expert at the US Council on Foreign Relations, who also believes it may have been from the S-300 system.
“We know that Russia uses the S-300 for ground attacks, although it is an air defense system, but Ukraine also uses it for air defense against cruise missiles,” he added.
Dr. Justin Pronk, a senior fellow at the Rossi Research Center, agrees that it could be from the S300 system, but there isn’t enough evidence to identify it yet.
The state-run RIA Novosti news agency quoted a Russian military expert as saying that Russian ballistic missiles are unable to reach Polish territory.