MOSCOW — A day after Prime Minister Vladimir Putin suggested that protesters who gather routinely in central Moscow should “”have a club on the head,”” riot police on Tuesday broke up a crowd of about 2,000 opposition supporters and onlookers and arrested scores of people.

The clash was part of a ritual that has seen demonstrators gather on the 31st day of the month in Triumfalnaya Square to press for the right of free assembly as enshrined in Article 31 of the Russian Constitution.

“”Permission from local authorities is needed”” for a demonstration, Putin said in an interview published Monday by Kommersant, a popular daily newspaper. “”If you come out without permission, have a club on the head, that is all.

“”If (their) goal is to compel the authorities to make concessions, and if it happens, then they will find another pretext for provocations and that is all there is to it,”” said Putin. “”And this will go on forever.””

Protesters maintain that Article 31 allows them to gather without seeking government permission. The Kremlin cites a later law that says demonstrators must receive approval to gather from officials, who can also dictate where the rally is held.

Authorities have sought with some success to frustrate the gatherings in Triumfalnaya, holding an auto show in the square July 31 and a blood drive by pro-Kremlin youth accompanied by loud music on May 31.

On Tuesday, metal fences surrounded the area after the government announced a construction project, forcing demonstrators to gather on the edge of the square.

While the protesters chanted “”Down with the police state!”” and “”Russia without Putin,”” riot police broke into the crowd, separated it into smaller groups and began making arrests.

“”Do you see this old girl with a poster?”” one officer said to a comrade. “”Let’s go get her, she is too loud.””

“”No, she is too big and I hate messing with old women!”” replied his fellow officer, dressed in a black helmet and black riot gear. “”Let’s get this tall guy in the gray jacket, the one on the right with glasses on.””

And off they went for the skinny young man in horn-rimmed spectacles holding a sign marked with the numerals 31. The sign went down on the asphalt and the young man into the police bus.

Valery Nadezhdin came to the square for the fifth or sixth time and three times he was arrested, he said. The 42-year-old business manager said that he was infuriated by Putin’s remark about the stick on the head.

“”They want to threaten us with tough actions,”” he said. “”But that only makes more and more eager to come here in protest against the unconstitutional actions of the authorities.””

“”When I first came here last year there were only several dozen demonstrators,”” said Nadezhdin. “”Today there are more than 1,000 of us and our ranks are growing.””

A group of young men shouting “”This is our city”” broke through a line of riot police and several yards later ran into another helmeted line that pushed them back. This went on for about an hour or so until dusk fell.

A source in Moscow law enforcement told Interfax news agency that about 100 people were arrested.

Nadezhdin ended up on the last police bus leaving the square. “”Freedom, freedom!”” he shouted through the bars in the open bus window.