Russian security forces fired on an armed gang of criminals in the centre of the occupied Ukrainian city of Kherson late on Saturday and "neutralised" them, Tass news agency reported.

Kherson, in the south of Ukraine, was occupied by Russian troops shortly after the February attack started and Kyiv is vowing to retake it.

"A group of armed persons that had been identified put up resistance. Russian security forces quickly went to the site and neutralised the criminals," Tass cited a security source as saying. There were no civilian casualties, the source added.

The clash took place on Ushakov Avenue, in the centre of Kherson, Tass said.

RIA news agency earlier cited a security source as saying the gang involved had been a "sabotage and reconnaissance group" but gave no details.

Video posted to Twitter showed what appeared to be Russian forces firing a heavy machine gun from an armoured car towards a target that could not be seen. Fire from a smaller calibre guns could also be heard.

The person taking the video said the clash was taking place in the centre of Kherson. Reuters was not immediately able to verify the video was authentic. (Reuters)