Reserve Polish Navy commander Maksymilian Dura said the missile could have changed course after sustaining damage, possibly from Ukrainian air defenses.
He said another possibility was that Russian forces had intentionally programmed the weapon to fly toward Polish territory.
The Operational Command of Poland’s Armed Forces said an unidentified object was detected in Polish airspace at 3:40 a.m. on Thursday.
An F-16 fighter jet was sent to identify and intercept it. The object disappeared from tracking systems at 3:46 a.m.
The military later located its probable crash site near the village of Tarnawa-Kolonia in the eastern Lublin province, close to Poland’s border with Ukraine.
A senior Polish defence official confirmed on Thursday that a Russian Kh-101 cruise missile entered Poland's airspace during a massive overnight Russian attack on Ukraine before crashing in a field in the country's east.
The Kh-101 is a long-range, air-launched cruise missile used by Russia to strike targets inside Ukraine.
Polish authorities have not yet established whether the missile entered the country because of a technical failure, damage sustained in flight or deliberate Russian action.
Prime Minister Donald Tusk told reporters that there was no indication Poland had been the intended target.
Tusk also said Polish forces had been prepared to shoot down the missile if it had posed a direct threat to populated areas.
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Source: IAR, PAP, polskieradio24.pl