Ukraine has lost over 40% of the territory in Russia's Kursk region that it captured 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 per cent of the territory captured in Russia’s Kursk region as Russian forced mount waves of counter assaults.

Faced with waves of counterattacks from nearly 60,000 Russian troops, Ukraine has lost more than 40% of the territory it once controlled in its August invasion of Kursk, Reuters reported, citing a member of the Ukrainian General Staff.

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.

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).

The deal comes at a tense moment in the Ukraine conflict, with Kyiv firing British and US-supplied long-range missiles into Russia and Moscow firing a hypersonic missile at its neighbour.