Police disperse opposition members in the park around Chistiye Prudy, or Clear Ponds, in Moscow early Wednesday, May 16, 2012. Since the middle of last week, opposition activists have tested authorities and themselves by maintaining an around-the-clock presence in a corner of the park that runs down the middle of Chistoprudny Boulevard, near the pond that gives the street its name. (AP Photo/Alexei Nikolayev) (Alexei Nikolayev/AP)

Police swept into a new gathering of political protesters Wednesday evening, pushing into a plaza where the demonstrators had established a base hours before and carting away the leaders.

An angry crowd of about 1,000 jeered at the police and tried to block their buses before being shoved aside.

The melee erupted quickly on a warm spring evening that had been completely calm. As the opposition crowd was listening to lectures, singing songs and generally enjoying the last hours of sunlight, the few police officers in sight had seemed prepared to let the gathering go on.

But then riot police suddenly poured in.

Police announced that catering or serving food without a license in a public park was illegal. All food was confiscated, and several protesters were detained. When the crowd reacted, the police began to move through the area in force.

What had been a mood inclined toward peaceful action turned to bitterness and anger. The crowd had been unlikely to stay because the city had forbidden tents at the site. But after the raid, protesters chanted their intention to remain.

Freelance journalist Andrei Novichkov complained that police officers intentionally broke the fingers of several journalists, himself included.

It was the second police raid of the day. In the early morning, an encampment of occupiers had been cleared from a site in Chistye Prudy. In that sweep, the protesters put up no resistance.

As soon as the occupiers at Chistye Prudy had been dispersed, word went out on Twitter to gather at the new site, by the Barrikadnaya metro station, named for the barricades of Russia’s 1905 revolution. That uprising a century ago led to Russia’s first constitution and political reform, and some commentators have suggested parallels between then and now, as an awakened opposition maneuvers against the firmly entrenched government of President Vladimir Putin.

“We’re just trying to get together,” said Ilya Yashin, one of the chief opposition organizers, as he took a noontime break from riding his bicycle around the fountain in the middle of the green space. “Look, this is our city.”

Yashin was among those later detained by police. The van he was put in stopped several blocks away, with a flat tire.

The Barrikadnaya green space — more of a plaza than a park — is on the other side of the city center from Chistye Prudy. It sits just off the Garden Ring Road, with the Moscow Zoo close by to the north and the main U.S. Embassy building a few doors down to the south.

Yashin had joked that maybe U.S. Ambassador Michael McFaul should put up a sign saying this was American territory. From the beginning of the protests, Russian government officials and television news programs have accused the United States of providing support to the demonstrations, a charge that the protesters themselves love to mock.

But Yashin was furious at the Chistye Prudy sweep, as were many others. Police, who were enforcing a court order, had promised they would not move until noon. Instead, they struck at 5:30 a.m.

“It’s just more proof that the word of a police officer in Russia means nothing,” said Yashin. He said he arrived at Chistye Prudy just as the sweep there was concluding.

At Barrikadnaya, people filtered in and out all day. A crowd of as many as 1,000 had formed by the time the sun began to set. Art was on display, protest songs were sung and inveterate talkers held forth. Lecturers illuminated small knots of listeners on topics such as “Political Violence and the Experience of Urban Freedom,” “Homophobia in the Law” and “What Russian Education Expects.”

Garry Kasparov, a former world chess champion who has turned to opposition politics, attracted a big circle of people when he arrived. Boris Nemtsov, another liberal political veteran, also came by. But neither is a leader of this Twitter-driven movement, and it was not a crowd that wanted to hear seven-point programs.

The quick move to Barrikadnaya — and the prospect that the police would force other moves down the line — raised the question of whether the protesters had a plan, or needed one. In St. Petersburg on Wednesday, veteran liberal politician Grigory Yavlinsky met with a small number of protesters who had organized a “people’s walk” near St. Isaac’s Cathedral, and urged them to focus on specific objectives.

“People’s walks should have a political meaning; they can’t be without a goal,” he said, according to the Interfax news agency. That goal, he said, should be electoral victory.

But the generally law-abiding nature of the latest actions, and the absence of the banners and speeches and lists of demands that would characterize them as political demonstrations in the eyes of the law, seemed at times to leave authorities here at a loss on how to respond.

Police officials said during the day Wednesday that people were free to go to a park or stroll along boulevards. Then they swept in as darkness fell, citing a previously unenforced law on eating in a public space. The move appeared likely to provoke more action by the opposition.

A group of artists who call themselves the Nomadic Modern Art Museum planned a walk here Saturday, ostensibly about art but with the backing of a movement called For Human Rights.

But if walking is one thing, camping is another.

“Putting up tents is not the kind of activity allowed in the city,” Alexei Maiorov, the head of the Moscow regional security department, told Interfax. “Those who want to put up tents and organize camps can go camping. It’s warm, and it’s May, and the weather is good for that.”