Poland's president says missile that killed two was likely fired by Ukraine in defense against Russian attack. (Photo: CNN)

(CNN) — The leaders of Poland and NATO said the missile that killed two people in Polish territory on Tuesday was likely fired by Ukrainian forces defending their country against a barrage of Russian strikes, and that the incident appeared to be an accident.

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

On Wednesday, Polish President Andrzej Duda told a press conference that there was a “high chance” it was an air defense missile from the Ukrainian side and likely had fallen in Poland in “an accident” while intercepting incoming Russian missiles.

“There is no indication that this was an intentional attack on Poland. Most likely, it was a Russian-made S-300 rocket,” Duda said in a tweet earlier Wednesday.

Both Russian and Ukrainian forces have used Russian-made munitions during the conflict, including the S-300 surface-to-air missile system, which Kyiv has deployed as part of its air defenses.

The incident in Poland, a NATO country, prompted ambassadors from the US-led military alliance to hold an emergency meeting in Brussels Wednesday.

NATO Secretary General Jens Stoltenberg too said there was no indication the incident was the result of a deliberate attack by either side, and that Ukrainian forces were not to blame for defending their country from Russia’s assault.

“Our preliminary analysis suggests that the incident was likely caused by the Ukrainian air defense missile fired to defend Ukrainian territory against Russian cruise missile attacks,” Stoltenberg said. “But let me be clear, this is not Ukraine’s fault. Russia bears ultimate responsibility, as it continues its illegal war against Ukraine.”

Stoltenberg also said there were no signs that Russia was planning to attack NATO countries, in comments that appeared to be intended to defuse escalating tensions.

News of the incident overnight led to a flurry of activity thousands of miles away in Indonesia, where US President Joe Biden convened an emergency meeting with some world leaders to discuss the matter on the sidelines of the G20 summit.

A joint statement following the emergency meeting at the G20 was deliberately ambiguous when it came to the incident, putting far more focus on the dozens of strikes that happened in the hours before the missile crossed into Poland.

Duda and Stoltenberg’s comments tally with those of two officials briefed on initial US assessments, who told CNN it appeared the missile was Russian-made and originated in Ukraine.

The Ukrainian military told the US and allies that it attempted to intercept a Russian missile in that timeframe and near the location of the Poland missile strike, a US official told CNN. It’s not clear that this air defense missile is the same missile that struck Poland, but this information has informed the ongoing US assessment of the strike.

The National Security Council said that the US has “full confidence” in the Polish investigation into the blast and that the “party ultimately responsible” for the incident is Russia for its ongoing invasion.

Investigations at the site where the missile landed will continue to be a joint operation with the US, Polish President Duda said Wednesday. Ukrainian President Volodymyr Zelensky has called for Ukrainian experts to be allowed to the site.

Zelensky said Wednesday he did not believe that the missile was launched by his forces, and called for Ukrainian experts to play a part in the investigation. “I have no doubt that it was not our missile,” he told reporters in Kyiv.

Earlier Wednesday, a Zelensky adviser said the incident was a result of Russia’s aggression but did not explicitly deny reports that the missile could have been launched by the Ukrainian side.

“Russia has turned the eastern part of the European continent into an unpredictable battlefield. Intent, means of execution, risks, escalation — it is all coming from Russia alone,” Mykhailo Podolyak said in a statement to CNN.

A spokesperson for the Ukrainian Air Force said on national television Wednesday that the military would “do everything” to facilitate the Polish investigation.

Earlier, Biden said that preliminary information suggested it was unlikely the missile that landed in Poland was fired from Russia, after consulting with allies at the G20 Summit in Bali.

“I don’t want to say that [it was fired from Russia] until we completely investigate,” Biden went on. “It’s unlikely in the minds of the trajectory that it was fired from Russia. But we’ll see.”

Kremlin Spokesman Dmitry Peskov said Wednesday that Russia doesn’t have “any relation” with the missile incident in Poland, and that some leaders have made statements without understanding “what actually happened.”

“The Poles had every opportunity to immediately report that they were talking about the wreckage of the S-300 air defense system missile. And, accordingly, all experts would have understood that this could not be a missile that had any relation with the Russian Armed Forces,” Peskov said during a regular call with journalists.

“We have witnessed another hysterical frenzied Russophobic reaction, which was not based on any real evidence. High-ranking leaders of different countries made statements without any idea about what actually happened.”

Estonian Prime Minister Kaja Kallas told CNN that NATO allies must “keep a cool head” in light of the incident.

“I think we really have to keep a cool head, knowing there might be a spillover effect, especially to those countries that are very close [to Ukraine],” Kallas told CNN’s Chief International Anchor Christiane Amanpour in an interview Wednesday.

The incident comes after Russia unleashed a barrage of 85 missiles on Ukraine Tuesday, predominantly targeting energy infrastructure. The bombardment caused city blackouts and knocked out power to 10 million people nationwide. Power has since been restored to eight million consumers, Zelensky later confirmed.

Ukrainians across the country were expected to face further scheduled and unscheduled power cuts Wednesday.