A Russian court on Wednesday sentenced a Saint Petersburg woman to eight days in jail for writing "no to war" on a ballot paper during the country's presidential election in protest at President Vladimir Putin's Ukraine campaign.

The three-day vote over the weekend saw Putin running unchallenged for a fifth Kremlin term, which would extend his rule until at least 2030.

The election was marred by ballot spoiling, with Putin warning in his victory speech that Russians who did so "have to be dealt with". 

Saint Petersburg's Dzerzhinsky district court said it ordered Alexandra Chiryatyeva to be jailed for eight days and fined 40,000 rubles ($440 euros). 

It said she was guilty of hooliganism and "discrediting the Russian armed forces". 

"Chiryatyeva took a voting ballot and with a red marker wrote 'no to war' at the back of it before placing it in the ballot box," the court said. 

"In this way, Chiryatyeva damaged state property and discredited the Russian armed forces."

The court said Chiryatyeva had done so on the final day of the three-day vote, when Russia's opposition groups called for protests against an election where Putin's win was inevitable. 

The vote was slammed by the West and independent Russian election observers as one of the most corrupt in post-Soviet history. 

Moscow has hugely cracked down on dissent as Russian troops fight in Ukraine.