NATO convened an emergency meeting of ambassadors in Brussels on Wednesday after a missile crashed near the Polish town of Przewodow on Tuesday, killing two people.
"We have no indication this was the result of a deliberate attack, and we have no indication that Russia is preparing offensive military attacks against NATO," the military alliance's Secretary General Jens Stoltenberg said after the meeting.
An investigation is ongoing but preliminary analysis “suggests the incident was likely caused by a Ukrainian air defence missile fired to defend Ukrainian territory against Russian cruise missile attacks”, Stoltenberg added.
However, Stoltenberg noted that the incident happened as Russia launched a "wave of indiscriminate missile attacks" across Ukraine on Tuesday.
"Let me be clear, this is not Ukraine's fault," he said. "Russia bears ultimate responsibility as it continues its illegal war against Ukraine."
Minutes earlier, Polish President Andrzej Duda also said that the missile crash was most likely an "unfortunate accident" and not an "intentional attack."
Poland is one of 30 members of the NATO military alliance. Each member state has agreed to defend each other against attacks from countries outside the bloc.
The European Union has also pledged support to Poland. Russia has denied any involvement in the missile strike.
Russia's defense ministry said photos of the wreckage in Poland "were unequivocally identified by Russian military experts" as being from an S-300 air defense system, as opposed to one of its own missiles. It did not provide further evidence.
Speaking to reporters in Russia on Wednesday, Kremlin spokesperson Dmitry Peskov accused some countries of making "baseless claims" about the missile incident and said the US response has been more measured in comparison.
US officials stated that initial findings suggested the missile was fired by Ukrainian forces at an incoming Russian missile, the Associated Press reported.
ZZ/PR