US President Joe Biden says preliminary information contests whether a missile that killed two people in Poland was fired from Russia.
Ukranian authorities say the missile was fired from Russia.
Biden says leaders at the G20 summit in Bali have agreed to support an investigation to find out exactly what happened.
Asked about claims that the blast was linked to Russia, Biden said: "There is preliminary information that contests that. I don't want to say that until we completely investigate it but it is unlikely in the lines of the trajectory that it was fired from Russia but we'll see".
Earlier, polish president Andrzej Duda said they have no definite evidence of who fired the rocket that fell on Przewodow.
Duda said what happened was a once off incident, and there are no indications that there will be a repeat of the incident.
It is very likely Poland will activate NATO's Article 4 at Wednesday's NATO meeting, he says. NATO ambassadors will meet at the request of Poland.
Two people died in the blast in a Polish village near the border with Ukraine on Tuesday, firefighters said.
The explosion occurred after Russia hammered cities across Ukraine with missiles on Tuesday, attacks that Kyiv said were the heaviest wave of missile strikes nearly nine months into its invasion of its neighbour. Some hit the western city of Lviv, less than 80km from the border with Poland.
The Associated Press cited a senior US intelligence official as saying the blast in the eastern Polish village of Przewodow was caused by Russian missiles crossing into Poland, a member of the Western military alliance NATO. Officials from NATO countries Norway, Lithuania and Estonia said they were trying to find out more information.
Russia's defence ministry said no strikes occurred against targets near the Ukrainian-Polish border that had been carried out by Russian weapons, IFX news agency reported.
Look back over RNZ's updates:
- Reuters / BBC