At the height of the campaign, Ukrainian forces controlled some 500 square miles of Russian territory. Now they hold just a small sliver of land along the border.

A Russian service member walks past destroyed buildings in the town of Sudzha, which was recently retaken by Russia's armed forces in the course of Russia-Ukraine conflict in the Kursk region, Russia,

The BBC has received extensive accounts from Ukrainian troops, who recount a "catastrophic" withdrawal in the face of heavy fire, and columns of military equipment destroyed and constant attacks from swarms of Russian drones.