Ukraine has lost over 40% of the territory in Russia's Kursk region that it rapidly seized in a surprise incursion in August as Russian forces have mounted waves of counter-assaults, a senior Ukrainian military source said.

Ukraine has lost over 40 percent of the territory in Russia's Kursk region that it rapidly seized in a surprise incursion in August as Russian forces have mounted waves of counterassaults, a senior Ukrainian military source has said.

The Kursk offensive was the first ground invasion of Russia by a foreign power since World War Two and caught Moscow unprepared.