NATO member Poland and the head of the military alliance both said Wednesday that a missile strike in Polish farmland that killed two people appeared to be unintentional and was probably launched by air defenses in neighboring Ukraine. Russia had been bombarding Ukraine at the time in an attack that savaged its power grid.

“Ukraine’s defense was launching their missiles in various directions and it is highly probable that one of these missiles unfortunately fell on Polish territory," said Polish President Andrzej Duda. “There is nothing, absolutely nothing, to suggest that it was an intentional attack on Poland.”

NATO Secretary-General Jens Stoltenberg, at a meeting of the 30-nation military alliance in Brussels, echoed the preliminary Polish findings. Ukrainian President Volodymyr Zelenskyy, however, disputed them and asked for further investigation.

The assessments of Tuesday's deadly missile landing appeared to dial back the likelihood of the strike triggering another major escalation in the nearly 9-month-old Russian invasion of Ukraine. If Russia had targeted Poland, that could have risked drawing NATO into the conflict.

Still, Stoltenberg and others laid overall but not specific blame on Russian President Vladimir Putin’s war.

“This is not Ukraine’s fault. Russia bears ultimate responsibility,” Stoltenberg said.

Zelenskyy told reporters he had “no doubts” about a report he received from his top commanders “that it wasn’t our missile or our missile strike.” Ukrainian officials should have access to the site and take part in the investigation, he added.

“Let’s say openly, if, God forbid, some remnant (of Ukraine's air-defenses) killed a person, these people, then we need to apologize,” he said. "But first there needs to be a prob, access - we want to get the data you have.”

On Tuesday, he had called the strike “a very significant escalation.”

Before the Polish and NATO assessments, U.S. President Joe Biden had said it was “unlikely” that Russia fired the missile but added: “I’m going to make sure we find out exactly what happened.”

A Russian Defense Ministry spokesman in Moscow said no Russian strike Tuesday was closer than 35 kilometers (22 miles) from the Ukraine-Poland border. The Kremlin denounced Poland’s and other countries’ initial response and, in rare praise for a U.S. leader, hailed Biden’s “restrained, much more professional reaction.”

“We have witnessed another hysterical, frenzied, Russo-phobic reaction that was not based on any real data,” Kremlin spokesman Dmitry Peskov said.

Later Wednesday, Russia’s Foreign Ministry summoned the Polish ambassador in Moscow; the discussion reportedly lasted about 20 minutes.

The Polish president said the missile was probably a Russian-made S-300 dating from the Soviet era. Ukraine, once part of the Soviet Union, fields Soviet- and Russian-made weaponry and has also seized many more Russian weapons while beating back the Kremlin’s invasion forces.

Russia's assault on power generation and transmission facilities Tuesday included Ukraine’s western region bordering Poland. Ukraine’s military said 77 of the more than 90 missiles fired were brought down by air defenses, along with 11 drones.

The countrywide bombardment by barrages of cruise missiles and exploding drones clouded the initial picture of what happened in Poland.

“It was a huge blast, the sound was terrifying." said Ewa Byra, the primary school director in the eastern village of Przewodow, where the missile struck. She said she knew both men who were killed - one was the husband of a school employee, the other the father of a former pupil.

Another resident, 24-year-old Kinga Kancir, said the men worked at a grain-drying facility.

“It is very hard to accept," she said. “Nothing was going on and, all of a sudden, there is a world sensation.”

In Europe, NATO members called for a thorough investigation and criticized Moscow.

“This wouldn’t have happened without the Russian war against Ukraine, without the missiles that are now being fired at Ukrainian infrastructure intensively and on a large scale,” said German Chancellor Olaf Scholz.

Swaths of Ukraine were without power after the aerial assault. Zelenskyy said about 10 million people lost electricity, but tweeted overnight that 8 million were subsequently reconnected. Previous strikes had already destroyed an estimated 40% of the country’s energy infrastructure.

Ukraine said the bombardment was the largest on its power grid so far.

A Washington-based think tank, the Institute for the Study of War, said Ukraine’s downing of so many Russian missiles Tuesday “illustrates the improvement in Ukrainian air defenses in the last month,” which are being bolstered with Western-supplied systems. Sweden said Wednesday that an air defense system with ammunition would form part of its latest and largest package of military and humanitarian aid to Ukraine, worth $360 million.

The U.S. has been Ukraine's largest supporter, providing $18.6 billion in weapons and equipment. U.S. Defense Secretary Lloyd Austin said flows of U.S. weapons and assistance would continue “throughout the winter so that Ukraine can continue to consolidate gains and seize the initiative on the battlefield.”

Army Gen. Mark Milley, chairman of the U.S. Joint Chiefs of Staff, said he tried to speak to his Russian counterpart Wednesday, but those efforts were not successful. Milley didn’t elaborate on the efforts, but the lack of communications, at a time when there were questions about whether Russia had struck a NATO ally, raises concerns about high-level U.S.-Russian communications in a crisis.

The Russian attacks followed days of euphoria in Ukraine sparked by one of its biggest military successes - the retaking last week of the southern city of Kherson.

With its battlefield losses mounting, Russia has increasingly resorted to targeting Ukraine’s power grid as winter approaches.

Russian attacks in the previous 24 hours had also killed at least six civilians and wounded another 17, a senior official, Kyrylo Tymoshenko, said Wednesday.

Lviv Gov. Maksym Kozytskyy said two of three Russian missiles hit critical energy infrastructure in the western province. Power was restored to about 95% of the province, he said, but only 30% of consumers can use electricity at the same time.

Power shortages caused extensive train delays extending into Wednesday, but there were no cancelations because diesel locomotives were pressed into service, rail officials said.

Kyiv resident Margina Daria said Tuesday’s strikes knocked out cellphone service in her area.

“We have already adapted to life without light, because we have scheduled outages every day, but without communication it was quite disturbing,” she said. “There was no way to even tell our families that we were OK.”