Russian police have arrested dozens of anti-government protesters in Moscow and St. Petersburg during rallies in support of the freedom of assembly.

About 100 people staged a peaceful sit-in in Moscow's central Triumfalnaya square Sunday calling for the implementation of Article 31 of the Russian constitution which guarantees freedom of assembly.

Police arrested about 40 of the demonstrators when they started to march on a nearby street.

Earlier in the day, police had said they would not detain protesters as long as they did not pose a risk to other people.

In St. Petersburg, police detained at least 20 people during an opposition gathering there.

Russian authorities often deny permission for demonstrations in major venues, such as Triumfalnaya Square in Moscow, and break up any unsanctioned rallies.