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 organizations, some buses, are bringing massive amounts of people."