Polish MiG-29 fighter aircraft intercepted a Russian reconnaissance plane over the Baltic Sea on Thursday in the second such incident this week, Polish Defense Minister Wladyslaw Kosiniak-Kamysz said.

Poland's army said on Wednesday that Polish jets had intercepted a Russian aircraft flying a reconnaissance mission in international airspace over the Baltic Sea on Tuesday without a filed flight plan and with its transponder turned off.

"Today MiG-29s intercepted a Russian reconnaissance plane over the Baltic Sea," Kosiniak-Kamysz said, describing it as just like the incident on Tuesday.

He gave no further details.

Countries on NATO's eastern flank have been on high alert for potential airspace incursions since September when three Russian military jets violated Estonia's airspace for 12 minutes, days after more than 20 Russian drones had entered Polish airspace.