July 3 (Reuters) - A Ukrainian military spy official said on Wednesday that a fire on a Russian warship in the Baltic Sea in April was caused by a joint operation conducted by his GUR agency and a pro-Kyiv Russian military group.

On April 7, the Serpukhov missile ship stationed in the Kaliningrad region was set on fire, the GUR military spy agency said at the time. It did not claim responsibility earlier.

Andriy Yusov told Reuters the operation was conducted in tandem with the Freedom of Russia Legion. (Reporting by Tom Balmforth, writing by Yuliia Dysa, Editing by Alex Richardson)