Russian police detained 176 people on Saturday at protests against Moscow's military operation in Ukraine, an NGO said.
OVD-Info, which monitors arrests during protests, said police had detained at least 176 people during demonstrations in 14 cities in Russia.
An AFP journalist in Moscow witnessed more than 20 people detained by riot police under heavy snowfall in the capital's central park Zaryadye, a short distance from the Kremlin.
Police escorted away people sitting on park benches or just standing around without explaining the reasons for the detention, the reporter said.
One of the detained women held a bouquet of white tulips, while another several times exclaimed "No to war in Ukraine!" as she was being taken away.
A national sit-in on Saturday against what Moscow calls its "military operation" in Ukraine was announced on social media by activists in around 30 Russian cities.
The organisers said in a statement they wanted to protest "the collapse of (Russia's) economy", against Russian President Vladimir Putin and to demand freedom for jailed Kremlin critic Alexei Navalny.
"Russia deserves peace, democracy and prosperity," they said.
In Russia's second city, Saint Petersburg, AFP saw multiple arrests near the city's Legislative Assembly where around 40 people gathered, although it was unclear how many were there to protest.
"Nobody will come, all the active ones were detained at previous protests," said 30-year-old Sergei Gorelov, who said he came to "take a look and show support if necessary".
"I just came to stand around, to somehow express my protest to everything that is happening. It's scary to protest actively," Galina Sedova, 50, told AFP at the scene.
Protesters risk fines and possible prison sentences by taking to the streets.
OVD-Info says that over 15,000 people have been detained at rallies across the country to protest Russian military action in Ukraine, which was launched on February 24.
