"We know for sure that a Russian missile attack on Ukraine continued throughout the day, but at the moment, we have no definite evidence of who fired that rocket. Investigations are ongoing," he told reporters.
Duda also reported that U.S. experts would join the investigation into the incident.
"At the moment, there is nothing to indicate that there should be any more such events. At the moment, we can say that what happened was an isolated case. There is nothing to indicate that there could be more," the Polish leader asserted.
Polish media reported on Tuesday that two missiles hit the town of Przewodów, killing two civilians.
The Russian Defense Ministry denied reports of alleged missile strikes on Polish territory for its part, calling them a "deliberate provocation aimed at escalating the situation."
The Pentagon urged not to speculate or hypothesize about a possible response to the situation in Poland, which is part of NATO.