Dozens of opposition activists remain camped on a central Moscow square, despite police arresting some 20 fellow protesters overnight.
Opposition leader Ilya Yashin was among those detained.
The protesters moved to Kudrinskaya Square on May 16 after riot police uprooted them from another Moscow site where they had been camped for a week.
The sit-in demonstrations are part of a so-called "unlimited" protest, which the opposition launched after violent clashes between demonstrators and police on May 6, the day before Vladimir Putin was sworn in for a third term as Russia's president.
Pro-opposition television presenter Ksenia Sobchak, a driving force behind the sit-ins, visited the square following the arrests.
"At the moment I think it's important to be here, and we'll see what happens, what [the police] are planning and whether they keep their promises this time on not dispersing the people who are gathered here," she told journalists.
Sobchak said on her Twitter account that local district officials -- many of whom belong to the opposition -- had legalized the sit-in by granting it the status of a "festival."
Most of the remaining 40 to 50 protesters have been sitting on benches. Some were seen clearing the square of rubbish or joining in morning exercises.
'Pretty Harsh' Police Action
Police have said protesters could stay on Kudrinskaya Square overnight as long as they did not damage the lawn.
Police say the detentions were made after they tried to investigate deliveries of food to the activists and an attempt to set up a field kitchen.
Opposition activist Aleksei Sakyerto accused the police of using force.
"I saw how the riot police took people away [and] how people tried to fight back," he said.
"It seemed to me to be pretty harsh. We saw a huge chunk of hair laying here right on the asphalt, but we didn't see anything else -- we just saw how they harshly took people away."
All those detained have been released, except for Yashin and another opposition figure.
Yashin's lawyer says the activist could face up to 15 days in prison.
The protesters are seeking to call attention to alleged electoral fraud in last December's parliamentary polls, the March presidential poll, high-level corruption, and what they see as the damage Putin's continued rule is inflicting on Russia.
Putin has been in power as president or prime minister for the past 12 years.
The week-long sit-in at Moscow's upscale Chistiye Prudy district was dispersed after a court, acting on complaints from local residents, ordered the camp dismantled.
City officials also claim the demonstrators caused 20 million roubles ($646,000) worth of damage to the park.
Based on reporting by Reuters, AP, and AFP