The FSB said the reporter would be placed on Russia’s wanted list. Under Russian law, the maximum penalty for illegally crossing the border is five years in prison.

The ministry condemned the actions of American journalists who reported from Kursk after Ukrainian forces took control of the region and complained that an American private military company was operating there as well.

The strikes, apparently aimed at stymieing a Russian counterpush, could mean that Kyiv intends to seek a foothold in the region.

Ukraine now controls 444 square miles of Russian territory.

Gen. Oleksandr Syrskyi’s statement is the first public comment from a Ukrainian military official on the gains of the lightning incursion that has embarrassed the Kremlin.

The exact aims of the operation remain unclear, and Ukrainian military officials have adopted a policy of secrecy – presumably to ensure its success.