World leaders gathering at the G20 summit in Bali are trying to defuse a possible escalation in the months-long war in Ukraine after a “Russian-made” missile landed in NATO member Poland, killing two people.   

  The missile landed outside the rural Polish village of Przewodow, about four miles (6.4 kilometers) west of the Ukrainian border on Tuesday, around the same time as Russia launched its biggest wave of missile attacks on Ukrainian cities in more than a month .   

  The circumstances surrounding the incident, which marks the first time a NATO country has been directly hit during the nearly nine-month conflict, remain unclear.  It is not known who fired the missile or where it was fired from, although the Polish Foreign Ministry has described it as “Russian-made”.   

  Both Russian and Ukrainian forces have used Russian-made munitions during the conflict, with Ukraine deploying Russian-made missiles as part of its air defense system.   

  Speaking to reporters after an emergency meeting with G7 and NATO leaders on the sidelines of the G20 summit in Bali, Indonesia, US President Joe Biden said preliminary information suggested it was “unlikely” the missile was fired from the interior of Russia, but could not say definitively until the investigation was completed.   

  “We agreed to support Poland’s investigation into the explosion … And I’m going to make sure we understand exactly what happened,” Biden said, adding that the leaders expressed solidarity over the deaths of two people.  “Then we will collectively determine our next step as we investigate and move forward.  There was total unanimity among the people at the table,” he added.   

  Biden said he briefed others gathered about his discussions with Polish President Andrzej Duda and NATO Secretary General Jens Stoltenberg.   

  In comments earlier Tuesday, Duda noted that while it was unclear who launched the missile, it was “most likely” made in Russia.  “We are working calmly and in a very calm way,” Duda said during a speech from the National Security Office in Warsaw.   

  The Kremlin denied involvement in the blast, with the Russian Defense Ministry calling the Polish media reports, which first reported the deaths, “a deliberate provocation to escalate the situation,” according to a brief statement late Tuesday.   

  He added that photos of the debris published by Polish media “from the scene in the village of Przewodow have nothing to do with Russian weapons.”   

  Kremlin spokesman Dmitry Peskov told CNN he had no information about an explosion in Poland.   

  Polish Prime Minister Mateusz Morawiecki said on Tuesday that evidence suggested the missile that landed in Przewodów was a “one-off act” and there was no evidence of further missile strikes.   

  But while urging calm, Morawiecki said Poland would increase its military readiness and was considering triggering Article 4 of the NATO treaty.  Article 4 is a consultation method that allows members of the 30-nation alliance to bring an issue – usually security-related – to the North Atlantic Council, its decision-making body, for discussion.   

  Whatever the outcome of the Polish-led investigation, the incident has heightened long-standing concerns about the risk of battlefield miscalculation igniting NATO-Russia conflict.   

  The witness to the explosion described hearing a terrifying “whoosh” as the missile flew over the city and the force of the explosion shook nearby windows.   

  Video taken by a resident, which was geo-tagged and confirmed by CNN, shows a large plume of smoke in the center of the village.   

  At the site of the explosion, local media showed an image of a crater and an overturned farm vehicle.  CNN cannot independently confirm the photos.   

  In his speech, Duda said the US would send experts to investigate the site as part of a joint operation.   

  Speaking after speaking with Duda on Tuesday, NATO chief Stoltenberg said it was “important to document all the facts”.   

  “My condolences for the loss of life.  NATO is monitoring the situation and the Allies are consulting closely.  It is important to document all the facts,” Stoltenberg said in a statement.