Russian officials and commentators have shown little indication that Moscow is about to change course under new pressure.

Russia's Defense Ministry, meanwhile, said its forces downed at least 70 Ukrainian drones overnight into Tuesday morning. Among the areas targeted was the southwestern Voronezh region, which borders northeastern Ukraine. At least 24 people were injured there, Gov. Aleksandr Gusev said on Telegram.

Russia's nuclear rules say it can use atomic weapons if the country — or one of its allies — is attacked, especially if the attacker is a non-nuclear nation backed by a nuclear power. That clause could be seen as applying to Ukraine,