UPDATE 1-Two Polish airports have been shut due to military aviation operations

Polish airports in the cities of Radom and Lublin have been closed due to military aviation operations, the Polish Air Navigation Services Agency (PANSA) reported on Wednesday.

Polish military commanders said earlier that Polish and allied air forces had started operations because of Russia's attack on facilities located in neighbouring Ukraine. "At the request of the army, the Polish Air Navigation Services Agency has issued a directive regarding restrictions in Polish airspace, including the temporary closure of two airports in Radom and Lublin," Marcin Hadaj, the spokesman for PANSA, told private television channel TVN24.

"There are certain restrictions in the eastern part of the country, and aircraft in Polish airspace must avoid this area," he said, adding that the airports could be shut for "approximately an hour". He said the military would make the final decision.

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 just days after more than 20 Russian drones

entered Polish airspace. Polish jets intercepted

a Russian aircraft on Tuesday that was flying a reconnaissance mission in international airspace over the Baltic Sea without a filed flight plan and with its transponder turned off.