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Vladimir Putin is due to be sworn in for a fourth term as president of Russia on Monday after winning the last election in March.

He has been in power for 18 years, whether as president or prime minister, and opponents have likened his tenure to the reign of a tsar, or emperor.

Riot police confronted protesters against his rule in Moscow and other Russian cities on Saturday.

There have been fears of new unrest on Monday as he takes office.

The inauguration at the Kremlin in Moscow is likely to be lower-key than in 2012, AFP news agency reports.

Mr Putin is only expected to meet volunteers who took part in his election campaign, the agency says.

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Why were there protests?

More than 1,000 arrests are said to have been made in 19 cities across Russia on Saturday, nearly half of them in Moscow.

Mr Putin was re-elected president with more than 76% of the vote, his best ever election performance, but widespread irregularities were reported by some international observers. Allegations of ballot-rigging had dogged previous elections too.

The country's best-known opposition leader, Alexei Navalny, was barred from standing against Mr Putin, on grounds of a conviction for embezzlement which he denies and alleges was politically motivated.

Mr Navalny was arrested briefly as he tried to join Saturday's unauthorised protest rally in Moscow under the slogan "He's not our tsar".

Domestic opponents accuse Mr Putin of undermining democracy in Russia - a policy dubbed "managed democracy" - to keep genuine opposition parties out of parliament and ensure that he and his allies retain power indefinitely.

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Could Putin just go on and on?

First elected president in 2000, Mr Putin renewed his four-year term in 2004 before stepping aside in 2008 to serve as prime minister under his protege, Dmitry Medvedev, because by law he could only serve two consecutive terms.