Opponents of Russian President Vladimir Putin alleged that voters in Sunday's presidential election were being compelled to show up at polling stations in a Kremlin drive to ensure Putin's likely win is not tarnished by a low turnout.

Ivan Zhdanov, an aide to opposition leader Alexei Navalny, who is barred from running in the race, said Navalny supporters monitoring the vote reported people being bussed to polling stations by their employers.

"We would call this the 'shuttle bus election'," Zhdanov told a briefing. "Some organisations, some buses, are bringing massive amounts of people."

Kremlin officials privately acknowledge some voters are reluctant to show up and vote, even if they support Putin, because they believe his victory is already a foregone conclusion. The officials say though the vote will be fair.

Ella Pamfilova, head of the commission organising the vote nationwide, has said any fraud will be stamped out. She said those alleging the election was rigged were biased against Russia.

Reuters reporters at polling stations across Russia spoke to multiple voters who said they had been instructed by bosses or academic supervisors to vote. Many took photographs of themselves voting, saying they were needed as proof.

In one case, a senior election official inspecting a polling station said the photographs of voting should not be allowed, and ordered election staff there to stamp it out.