Ukrainian border guards repelled an incursion by a Russian sabotage and reconnaissance group in the northeastern region of Sumy on Monday, the governor of the Sumy region said.
Dmytro Zhyvytsky wrote on the Telegram messaging app that the Russian group entered Ukrainian territory under the cover of mortar shells, grenades and machine gun fire but retreated after the border guards fought back.
Reuters could not independently verify Zhyvytsky's account.
Russian forces crossed into the Sumy region shortly after Moscow invaded Ukraine on Feb. 24. Ukrainian forces retook control of the region on April 8 and have been bracing for further attacks.
More than 80 days after the invasion started, Ukraine has scored a series of successes, forcing Russia's commanders to abandon an advance on the capital Kyiv and making rapid gains around the second-largest city Kharkiv.
Moscow calls its actions in Ukraine a "special military operation" to rid the country of fascists, an assertion Ukraine and its Western allies say is a baseless pretext for an unprovoked war.
(Reporting by Pavel Polityuk, Writing by Alexander Winning, Editing by Timothy Heritage)