Ukrainian troops sprang one of the biggest surprises of the war by invading Russia's Kursk region last August, and Russia has taken more than seven months to eject them.

Russian forces have begun an assault on the town of Sudzha, the main population center in the Kursk region that was captured by Ukraine last year, a top Russian commander said on Tuesday. The advance puts Moscow on the verge of ending the first invasion of Russian territory since World War II.

Russian President Vladimir Putin has called on Ukrainian troops in the Russian region of Kursk to surrender, as diplomatic back-and-forth continues over a potential US-brokered ceasefire with Ukraine.