Critics of Vladimir Putin and his Kremlin regime have called for massive protests at Russian polling stations on Sunday, the final day of a presidential election that is guaranteed to cement his hardline rule.

The three-day vote has already been hit by Ukrainian bombardments and a series of incursions into Russian territory by anti-Putin sabotage groups. Early on Sunday, a drone attack caused a fire at a refinery at Slavyansk in the Krasnodar region of southern Russia, where officials said one person died of a heart attack, while two people died after drone strikes in the Russian city of Belgorod on Saturday, according to officials.

On Sunday morning the Russian defence ministry reported 35 Ukrainian drone incursions, including four in the Moscow region and two in the neighbouring Kaluga and Yaroslavl regions. More Ukrainian drones attacked in the Belgorod, Kursk and Rostov regions bordering Ukraine, and in the southern Krasnodar region, the defence ministry said.