Ukraine's intelligence directorate said on Sunday that an explosion in the Russian-occupied town of Melitopol killed at least three Russian servicemen in an attack it described as an "act of revenge" by local underground groups.

The blast occurred during a meeting on Saturday of Russian officers in the town, a hub of Russian forces in the south, the directorate within the defence ministry said in a statement.

"This act of revenge, carried out by representatives of the local resistance, took place in the New Post offices seized by the Russians," it said.

There was no mention of the incident from Russian officials. Reuters was unable to verify the Ukrainian statement.

The intelligence statement said the meeting on Saturday at the local military headquarters was attended by Russian National Guard and FSB intelligence service officers.

"As a result of the explosion at least three National Guard officers were killed at the headquarters," the statement said. "Information of other enemy losses is being clarified."

The statement said police converged on the area and a burned-out car was later seen being towed through the town.

Russia began a full-scale invasion of Ukraine in February 2022. Ukraine launched a counteroffensive in the south and east in early June, but has encountered strong resistance.

Ukraine's military has been increasingly active in attacking forces in Russian-held areas, but does not always acknowledge the strikes.

Ukrainian forces staged a missile attack on the Black Sea Fleet headquarters in Russian-annexed Crimea in September. Ukrainian media said an attack last week on the occupied town of Skadovsk in Kherson region also targeted Russian officers.

(Reporting by Ron Popeski; editing by Grant McCool)