MOSCOW, Russia - Russia on Monday officially registered incumbent Vladimir Putin as a candidate for the presidential election in March, a vote that he is all but certain to win.

The 71-year-old has led Russia since the turn of the century, clinching four presidential ballots and briefly serving as prime minister in a system where opposition has become virtually non-existent.

The Central Election Commission said it had registered Putin, who nominated himself, as well as right-wing firebrand and Putin-loyalist Leonid Slutsky as candidates for the vote.

The election will be held over a three-day period from March 15 to 17, a move that Kremlin critics have argued makes guaranteeing transparency more difficult.

Putin's spokesman, Dmitry Peskov, told Russian media on Monday the longtime leader would not take part in pre-election debates.

Following a controversial constitutional reform in 2020, Putin could stay in power until at least 2036.

Rights groups say that previous elections have been marred by irregularities and that independent observers are likely to be barred from monitoring the vote.

While Putin is not expected to face any real competition, liberal challenger Boris Nadezhdin has obtained the number of supporting signatures required to be registered as a candidate.

However, it is still unclear if he will be allowed to run, and the Kremlin has said it does not consider him to be a serious rival.