Russian police detained at least 20 people in the Russian capital on Monday after a protest against Moscow mayor Yuri Luzhkov, Russian media reported.
"There are over 20 (detainees) in the (police) bus," one of the organisers, Sergei Udaltsov, was quoted by Interfax as saying by telephone.
"We were cruelly beaten," Udaltsov told the Moscow Echo radio.
"Almost all of the detainees were dragged along, and many suffered," another known rights activist, Lev Ponomaryov, told Interfax.
The agency said that according to the police those arrested were facing charges of staging an unauthorized rally and disobeying police orders.
The anti-Luzhkov protest in central Moscow's Tverskaya square was joined by about 100 people.
The detentions came a month after police violently broke up an opposition protest in central Moscow and detained 100 people.