Russian police have detained at least 40 demonstrators, including opposition leaders, who attempted to go ahead with a banned political rally in central Moscow.

Among those detained was the Left Front leader Sergei Udaltsov and anti-corruption blogger Alexei Navalny.

In Lubyanka Square there is a small monument called the Solovetsky Stone, which represents the victims of Soviet oppression.

Up to 2,000 Muscovites gathered at the site to demand an end to Vladimir Putin's 13-year rule.

They laid flowers, not only to honour victims of the past, but as a warning that repression is returning.

The square was ringed by police, who informed the crowd the rally was an unsanctioned event and they should leave.

Earlier in the week, authorities had denied Russia's opposition permission to stage the rally.

Those who attended considered that decision unconstitutional.

Protesters, wrapped in scarves and fur hats because of the cold, chanted "Down with the police state" and "Russia without Putin".

"I don't know how many people are here but I am proud of each and every one of those who came here," Mr Navalny said.

"The main thing is that people are here, that they are expressing their view and showing that they exist.

"Obviously the authorities don't like attempts to carry out such protest actions and the development of the protest movement in general.

They don't like anything that threatens them."

Police eventually lost patience with the crowd and strode across the square hauling protesters away one by one.

About 40 people were detained and there were minor scuffles.

Mr Udaltsov and Mr Navalny, along with two fellow protest leaders, were released without charge hours later, indicating they had been detained to prevent them stirring up the protest crowd.

BBC/Reuters