Ukrainian forces have said they have accepted the surrender of the largest single group of Russian soldiers since the start of the war more than two years ago, as Kyiv’s military claimed to continue expanding its cross-border incursion.

A Ukrainian Security Service unit operating in Russia’s Kursk region took 102 Russian servicemen as prisoners-of-war, according to a person with knowledge of the operation, who asked not to be identified because the matter is sensitive.

The Russians were captured Wednesday in a sprawling underground complex, and had ample stocks of ammunition and supplies, the person said. Russia hasn’t commented.