Russia has made a rare admission, saying that a key air defence system and an air base in the Kursk region were hit by Ukraine with US-supplied Atacms missiles.
The defence ministry statement, which threatened retaliation, came a day after Ukraine said it had hit targets in the region.
Meanwhile Ukraine's air force said Russia launched a record 188 drones in a single attack on Monday night, damaging critical infrastructure.
Tensions have been high since the US reportedly allowed Ukraine to use Atacms missiles on targets inside Russia last week, in response to Russia deploying North Korean troops.