Ukrainian unmanned aerial vehicles hit a military airbase in Voronezh overnight into Tuesday, and witnesses heard at least 15 explosions, public broadcaster Polish Radio's polskieradio24.pl website reported.
Officials evacuated people from an apartment block nearby, after it was hit by falling drone debris which sparked a fire.
Voronezh's mayor said a state of emergency had been introduced in the city to repair the damage from the strike, according to the Reuters news agency.
Voronezh is a city of some 1 million people, located 250 km from the Ukrainian border, polskieradio24.pl noted.
The Voronezh air base houses some of Russia's fighter-bomber aircraft which are often deployed in air strikes on Ukraine, the Reuters news agency reported.
Tuesday is day 692 of Russia’s war on Ukraine.
Russia invaded Ukraine on February 24, 2022, launching the largest military campaign in Europe since World War II.
Source: polskieradio24.pl, Reuters