Police detained more than 200 opposition activists on Saturday for taking part in a wave of anti-Kremlin protests across Russia in support of jailed opposition leader Alexei Navalny, ahead of a presidential election in March, a monitoring group reported.

Under grey skies and intermittent rain, over two thousand people gathered in central Moscow's Pushkin Square and chanted "Russia will be free" and "Russia without Putin" before walking towards the Kremlin and parliament.

Police briefly detained a few people, but did not charge anyone. It was a different story at rallies in other cities however, and the OVD-Info monitoring group, a non-profit organisation, said at least 262 people had been detained in 27 towns.

In St Petersburg, Putin's home town, a Reuters witness saw riot police roughly detain at least 11 people. OVD-Info said at least 66 people had been detained in the city.

Navalny, who is serving a 20-day jail term for violating rules on public meetings, called the rally in Moscow and other cities to coincide with Putin's 65th birthday.

Putin, who has dominated Russia's political landscape for almost 18 years, is widely expected to run for what would be his fourth term.

Navalny hopes to run too, despite the central election commission declaring him ineligible due to a suspended prison sentence he says was politically-motivated.

One of the Moscow protesters held a homemade poster of Putin sitting on a mountain of banknotes, wearing a crown with the legend: "Happy Birthday you little thief!"

Others carried posters citing their right to protest, some waved Russian flags, and a few carried inflatable yellow ducks, a jokey reference to Navalny accusing Prime Minister Dmitry Medvedev of owning a lavish estate with a duck house.

Medvedev called the claims politically-motivated nonsense.

In St Petersburg, some 1,500 activists waving red and white banners gathered in a square before heading for the city's main street shouting "Putin is a thief" and "Free Navalny".

PROTESTS MORE MODEST IN SIZE

The size of Saturday's Moscow rally and others across Russia looked far more modest than Navalny-backed mass protests in March and June, which were widely recognised to be some of the biggest since 2012.

Many of the Moscow protesters were teenagers or in their twenties.

Carrying a yellow duck, Ulugbek Apsapayev, 17, said he had turned up because he wanted a better future for Russia.

"The duck is a sign that we support Alexei Navalny who also wants only good things for the country. But unfortunately we only have Vladimir Putin and his gang in power."

Putin is popular across the country however, especially outside major cities where his strong leadership style and tough foreign policy stance go down well. He is expected to confirm later this year that he will run for another six-year term.

Opinion polls show he would comfortably beat Navalny if the opposition leader was allowed to run. Navalny says such polls are meaningless because there is no fair political competition.

Putin spent his birthday taking congratulatory calls from other world leaders, and chaired a security council meeting.

Authorities had refused to approve most of Saturday's rallies, but Navalny says Russians' right to protest is enshrined in the constitution.

A Reuters reporter at a rally in the Urals city of Yekaterinburg saw police detain at least eight people among a crowd of over 1,000 protesters.