Russia on Wednesday accused Ukraine of a deadly blast in Poland, with Belgium saying it was probably caused by Kyiv's air defences firing at Moscow's incoming missiles.
The explosion in a farm building on Tuesday killed two people, leaving the village of Przewodow in shock and sparking international concern over a possible further escalation of the conflict.
Ambassadors from members of the NATO military alliance went into emergency talks in Brussels after Poland put its military on high alert in the wake of the blast and summoned Russia's ambassador.
"Based on the preliminary information available, the strikes are most likely a result of Ukrainian anti-aircraft systems that were engaged to take Russian missiles out of the sky," Belgian Defence Minister Ludivine Dedonder said in a statement.
US President Joe Biden had said it was "unlikely" the missile came from Russia, and the Kremlin said it had "nothing to do with" it.
"Photographs of the wreckage... were unequivocally identified by Russian military experts as fragments of a guided anti-aircraft missile of a Ukrainian S-300 air defence system," the Russian defence ministry said in a statement.
It added that "strikes were carried out on targets only on the territory of Ukraine and at a distance of no closer than 35 kilometres from the Ukrainian-Polish border."
But Ukrainian Foreign Minister Dmytro Kuleba earlier rejected as a "conspiracy theory" the idea that it may have been a Ukrainian missile.
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A statement from the Polish Foreign Ministry identified the missile as being made in Russia. But Poland's president, Duda, was more cautious about its origin, saying that officials did not know for sure who fired it or where it was made. He said it was “most probably” Russian-made, but that is being still verified. If confirmed, it would be the first time since the invasion of Ukraine that a Russian weapon came down on a NATO country.
(With AFP and AP inputs)