Col. Bartosz Okoniewski, deputy district prosecutor for military affairs at the District Prosecutor's Office in Poznań, western Poland, said the drone, found near Rusinowo, close to the Baltic seaside resort of Jarosławiec, carried a high-explosive fragmentation warhead fitted with a detonator.
The warhead was separated from the drone and destroyed on the beach on Tuesday evening for safety reasons, he said.
The drone was taken to a military facility for detailed examination, Okoniewski added.
Prosecutors said they were investigating the incident as an event endangering many people and property and involving the detonation of explosive material.
They are also investigating whether "an aircraft was used to cross the Polish border without authorisation."
Defence Minister Władysław Kosiniak-Kamysz said the drone may have previously flown over Lithuania, where authorities were searching for it and attempting to neutralise it, according to reports.
Kosiniak-Kamysz said the drone probably crossed Lithuania's border with Russia's Kaliningrad region before operating over the Baltic Sea.
Poland and Lithuania will investigate the incident jointly, Kosiniak-Kamysz told reporters.
(sp/gs)
Source: IAR/PAP