Russia started its final day of presidential voting on Sunday with Moscow accusing Ukraine of using air attacks to try to sabotage the election that is expected to keep President Vladimir Putin in power for another six years.

More than half of Russian voters have already gone to the polls in the first two days of the three-day-election, according to officials. The final day will test the strength of the country's opposition, which called for all its supporters to vote at the same time at noon, in an action dubbed "Noon Against Putin."

Sporadic protests have already marked the election but the latest developments in the war with Ukraine have cast a greater shadow on the vote so far. On Friday, Putin accused Kyiv of trying to disrupt the election with its intensified drone and missile attacks inside Russia and on Moscow-held territory in Ukraine. He also vowed to punish Ukraine.

Local Russian officials said early Sunday that Kyiv's forces continued their strikes on Russian regions bordering Ukraine.

Ukraine's President Volodymyr Zelenskiy did not address the reported attacks in his nightly video address on Saturday, but he thanked his military forces and intelligence "for the new Ukrainian long-range capabilities."

Kyiv regards the election taking place in parts of its territory controlled by Russia as illegal and void. Military analysts see the daily pounding by Kyiv that chiefly targets energy and other key infrastructure as an attempt to shake Russians' feeling of stability and undermine Moscow's war effort.

The Ukraine war has been the deadliest conflict in Europe since World War Two. None of the other three candidates on the ballot presents any credible challenge to Putin, 71, who dominates Russia's political landscape.

But the supporters of Putin's most prominent foe, the late Alexei Navalny, who died suddenly in an Arctic penal colony in February, called on people across Russia turn out to vote all at the same time at noon on Sunday in each of the country's 11 time zones.

The "Noon Against Putin" action, endorsed by Navalny's widow Yulia Navalnaya, is presented as a way for people to express opposition without the risk of arrest because they will be queuing up to vote legally. The Kremlin has warned people against taking part in unauthorised gatherings.

"Today we want to say to all of us - noon is the very beginning," the "Noon Against Putin" initiative wrote on their Telegram early Sunday.

"Yes, some of us are scared. Yes, the choice is not easy. But we are the people. And we will cope with both the choice and the responsibility."

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.

The Russian Central Election Committee said that more than 63 million voters had already gone to the polls by Saturday evening.