Ukraine and its Western supporters are openly arguing over who launched the missile that killed two civilians in Poland.

This may be the most significant rift in the war between Ukraine and its supporters, including the United States, and it comes at a crucial time as winter approaches, NBC News reported.

Although the U.S. and its allies called the incident an unfortunate accident, sharply divergent views on what happened threaten to undermine the united front that helped Kiev maintain steadfast military and diplomatic support from the West throughout the nearly nine-month war.

Ukrainian President Volodymyr Zelenskiy insisted that it was not their missile that hit Polish farmland, and the horrific incident raised the specter that NATO and its nuclear-armed members could be drawn directly into war.

The day before, Zelenskiy said he had been personally briefed on the matter by the Ukrainian military leadership, adding, "I have no reason to doubt them."

But President Joe Biden, commenting on the Ukrainian leader's claims, said, "This is not proof".

In fact, less than 24 hours after the incident, both NATO and Poland said it was probably a Ukrainian air defense missile designed to shoot down one of the Russian missiles.

"Let me be clear. It was not Ukraine's fault," NATO Secretary General Jens Stoltenberg told reporters at the alliance headquarters in Brussels. "Russia bears ultimate responsibility."

The White House quickly agreed, saying the U.S. saw nothing to contradict Poland's assessment that a Ukrainian air defense missile probably landed on its territory. At the Pentagon, Defense Secretary Lloyd Austin said the U.S. was still gathering information but agreed that the missile was probably Ukrainian.