Initial findings suggest that the missile that hit Poland was fired by Ukrainian forces at an incoming Russian missile, Associated Press reported on Wednesday, citing U.S. officials.

 President Joe Biden also said on Wednesday it was “unlikely” that that missile that killed two in NATO-ally Poland was fired from Russia, but he pledged support for Poland’s investigation into what it had called a “Russian-made” missile.

Biden spoke after he convened an “emergency” meeting of the Group of Seven and NATO leaders in Indonesia on Wednesday morning for consultations on the explosion that killed two people in the eastern part of Poland near the Ukraine border.

“There is preliminary information that contests that,” Biden told reporters when asked if the missile had been fired from Russia. “It is unlikely in the lines of the trajectory that it was fired from Russia, but we’ll see.”

Three U.S. officials said preliminary assessments suggested the missile was fired by Ukrainian forces at an incoming Russian missile amid a crushing salvo against Ukraine’s electrical infrastructure on Tuesday. The officials spoke on condition of anonymity because they were not authorized to discuss the matter publicly.

Ukraine still maintains stocks of former Soviet and Russian-made weaponry, including the S-300 air-defense missile system.

The president, who was awakened overnight by staff with the news of the missile explosion while in Indonesia for the Group of 20 summit, called Polish President Andrzej Duda early Wednesday to express his “deep condolences” for the loss of life. Biden promised on Twitter “full U.S. support for and assistance with Poland’s investigation,” and “reaffirmed the United States’ ironclad commitment to NATO.”