WATCH: Secretary Austin, General Milley echo Polish assessment of missile strike

Defense Secretary Lloyd Austin has echoed NATO member Poland by saying that a missile strike in Polish farmland that killed two people did not appear to be intentional 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.

Watch the briefing in the player above.

NATO Secretary-General Jens Stoltenberg has also echoed the preliminary Polish findings. He did so at a meeting of the 30-nation military alliance in Brussels.

At the Pentagon, Austin said the U.S. has confidence in Poland’s early assessment, but wants to let the investigation “play out.” He also said that Russia bears responsibility for the incident because of its invasion of neighboring Ukraine.

“Whatever the final conclusions may be, the world knows that Russia bears ultimate responsibility for this incident,” Austin said.

The initial assessments of Tuesday’s deadly landing of the Soviet-era missile 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 deliberately targeted Poland, that could have risked drawing NATO into the conflict.

READ MORE: Biden says it’s ‘unlikely’ the missile that hit Poland was fired from Russia

Ukrainian President Volodymyr Zelenskyy disputed the preliminary findings and demanded evidence. He told reporters he had “no doubts” about a report he said he had personally 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.

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.”

Three U.S. officials said preliminary assessments suggested the missile was fired by Ukrainian forces at an incoming Russian one. The officials spoke on condition of anonymity because they weren’t authorized to discuss the matter publicly. That assessment and Biden’s comments at the Group of 20 summit in Indonesia contradicted information earlier Tuesday from a senior U.S. intelligence official who told The Associated Press that Russian missiles crossed into Poland.

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, including air-defense missiles, and has also seized many more Russian weapons while beating back the Kremlin’s invasion forces.

READ MORE: Russian missile strikes cause power blackouts across Ukraine

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.

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, with repair crews laboring through the night. Previous strikes had already destroyed an estimated 40 percent of the country’s energy infrastructure.

Appearing with Austin, Gen. Mark Milley described Russia aerial bombardment of Ukraine’s civilian infrastructure as a war crime.