Vladimir Putin accused Ukraine on Friday of aiming to disrupt Russia's presidential election by shelling Russian territory and using 2,500 armed soldiers to try to pierce his country's borders, and vowed to punish Kyiv for its actions.

The first day of the election was also marred by disruptions including dye being poured into ballot boxes, a Molotov cocktail thrown at a polling station in Putin's home town, and reported cyber attacks.

Millions of Russians cast their ballots across the country's 11 time zones at the start of the three-day election.

The shadow of the Ukraine war fell across the election, with what Putin said was repeated shelling of Russia's western regions and an attempt by Ukrainian proxies to cross into Russian territory in two Russian regions.

"These enemy strikes will not remain unpunished," a visibly angry Putin said at a meeting of Russia's Security Council, which includes military and spy chiefs as well as the most powerful civilian state officials.

Putin said there had been four attacks on the Belgorod region and one on the Kursk region by armed Ukrainian proxies numbering about 2,500. He said they had 35 tanks and 40 armoured vehicles and that 60 percent of the soldiers were killed.

Ukrainian officials said earlier on Friday that Russian armed groups based in Ukraine who are opposed to the Kremlin carried out the attacks in the Belgorod and Kursk regions.

More than 114 million Russians are eligible to vote, including in what Moscow calls its "new territories" – four regions of Ukraine that its forces only partly control, but which it has claimed as part of Russia. Ukraine says the staging of elections there is illegal and void. (Reuters)