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

The Ukrainian source revealed that their forces initially controlled up to 1,376 square kilometres (531 square miles) of territory in Kursk but now hold around 800 square kilometres (309 square miles).

Ukrainian President Volodymyr Zelensky said Russia has deployed nearly 50,000 troops to Kursk, the southern Russian region where Kyiv launched its surprise counteroffensive in the summer.

Meanwhile, Ukraine's surprise incursion into Russia's Kursk region is faltering. Russian troops have pushed Kyiv's offensive backwards. Experts have questioned the success of the offensive, with one calling it a "strategic catastrophe" given manpower shortages faced by Ukraine.

Russia has amassed a large force of tens of thousands — including recently arrived North Korean troops — to carry out an assault on the Ukrainian positions in Russia’s Kursk region expected in the coming days,