US President Joe Biden has ruled out the possibility that the missile that killed two people in Poland was from Russia.
Asked by reporters whether the missile was fired by Russia, Biden declined to say until the investigation was complete.
The explosion at a grain facility near the Ukrainian border came as Russia launched a series of missile strikes targeting Ukraine's energy infrastructure.
This in turn sparked fears that the conflict would escalate, especially since Poland is a member of NATO.
Poland's foreign ministry said the rocket fell in Przewodów, a village about 6km from the border with Ukraine.
However, the Kremlin denied the claims although Polish officials said the missiles were Russian-made.
Meanwhile, in a separate report, Polish President Andrzej Duda said there was no authentic evidence about the mastermind who fired the missile.
