Poland has no concrete evidence showing who fired the missile that caused explosions in a village near the Ukrainian border, President Andrzej Duda said on Wednesday.
"We do not have any conclusive evidence at the moment as to who launched this missile. It was most likely a Russian-made missile, but this is all still under investigation at the moment," Duda told reporters.
Polish Prime Minister Mateusz Morawiecki earlier said at a press conference that Poland is investigating the explosions, with security forces and international experts on site.
Morawiecki added that Poland has decided to increase surveillance of its airspace, as he confirmed that Poland was studying the possibility of requesting consultations under Article 4 of the NATO military alliance treaty.
U.S. President Joe Biden said on Wednesday after meeting allies that they would support Poland in probing "exactly what happened" in a missile strike that hit Polish territory, but said preliminary information showed it was probably not fired from Russia.
"It is unlikely... that it was fired from Russia," Biden told reporters in Bali, where he has been attending the G20 Summit. "I'm going to make sure we figure out exactly what happened."
Meanwhile, NATO chief Jens Stoltenberg will also chair an emergency meeting of NATO ambassadors on Wednesday on the event, according to his spokesperson.