Government troops in eastern Ukraine have won back the port city of Mariupol from pro-Russian activists after heavy fighting.

Interior Minister Arseny Avakov said the security forces had successfully brought activist strongholds in the city "under control".

Five pro-Russian activists were reported killed and at least four government soldiers injured in the city. Activists elsewhere in the region have confirmed they now have three tanks, BBC News said.

The appearance of the tanks, filmed in various towns in the Donetsk region, sparked a row between Kyiv and Moscow, with Ukrainian President Petro Poroshenko protesting to his Russian counterpart, Vladimir Putin. Russia denied Ukrainian allegations that the tanks had entered Ukraine from its territory.

Hundreds of combatants and civilians have been killed since pro-Russian activists in the Donetsk and neighbouring Luhansk regions declared independence after holding referendums last month, which were deemed illegal by the government in Kyiv.