Polish President Andrzej Duda said late on Tuesday that Poland has no conclusive evidence showing who fired the missile that caused an explosion in a village near the Ukrainian border, the Reuters news agency reported.
Two people were killed in the explosion in Przewodow, about 6 km from the border with Ukraine, firefighters said. Media reports said the strike hit a grain-drying facility.
"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.
He added that it was very likely that Poland would request consultations under Article 4 of the NATO military alliance following the blast.
His comments came after the Polish foreign ministry confirmed that a Russian-made rocket had fallen on the village.
Duda spoke after Prime Minister Mateusz Morawiecki said that Poland would increase surveillance of its airspace following the incident.
"We decided to increase the combat readiness of selected units of the Polish armed forces, with particular emphasis on airspace monitoring," Morawiecki said.
A government spokesman had said earlier that Poland is putting some military units on a heightened state of readiness after the missile explosion.
"There has been a decision to raise the state of readiness of some combat units and other uniformed services," spokesman Piotr Muller told reporters after an emergency national security council meeting in Warsaw.