U.S. President Joe Biden told G7 and NATO partners that a missile blast in eastern Poland was caused by a Ukrainian air defence missile, a NATO source told Reuters on Wednesday.
The blast, which killed two people, raised global alarm that the Ukraine conflict could spill into neighbouring countries.
Ukraine blamed Russia. Russia denied its missiles struck Poland.
Biden told reporters in Indonesia on Wednesday that the missile was unlikely to have been fired from Russia.
NATO ambassadors were scheduled to hold an emergency meeting at 1000 CET (0900 GMT) to respond to the explosion at a grain dryer near the Ukrainian border, which occurred while Russia was firing scores of missiles at cities across Ukraine. (Reporting by Andreas Rinke, writing by Kirsti Knolle, editing by Paul Carrel)