Russian air defenses downed what authorities described as five Ukrainian balloons overnight, the defense ministry in Moscow said Thursday, as the sides kept up long-range strikes that have featured heavily in what has largely become a war of attrition.

Neither Russian nor Ukrainian officials have provided details about the secretive balloons, which Moscow authorities and media have reported on the battlefield in recent weeks. Ukraine’s military has been driving innovation since the war began in February 2022, notably adapting drones for wide use against the bigger Kremlin forces.