Russia's President Vladimir Putin will mount a counteroffensive to try to retake territory in the Kursk region captured by Ukrainian troops, but Russian forces will encounter "a difficult fight," CIA Deputy Director David Cohen said on Wednesday.

He told a national security industry conference that the significance of the Ukrainian incursion, which has overrun some 300 square miles (777 square kilometers) of the Russian province, remained to be seen.

Ukrainian forces crashed through Russia's western border into the Kursk region on Aug. 6 in a surprise offensive that is continuing.