KYIV, Oct 1 (Reuters) - Ukraine has encircled Russia's forces around a bastion that is critical for Moscow at the eastern town of Lyman, in an operation that is still under way, a Ukrainian military spokesperson said on Saturday.

Russia's forces at Lyman totalled around 5,000 to 5,500 soldiers, but the number of encircled troops may have fallen because of casualties and some soldiers trying to break out of the encirclement, said Serhii Cherevatyi, spokesperson for Ukraine's eastern forces. (Reporting by Pavel Polityuk Writing by Tom Balmforth Editing by Frances Kerry)