Russian opposition leader Lyubov Sobol has been detained ahead of an unauthorised protest in Moscow.
Ms Sobol was in a taxi about to set off for the rally when police officers dragged her into a black van, which swiftly sped off.
Protesters are gathering in the Russian capital after authorities disqualified a number of opposition candidates from standing in local elections.
Media reports suggest 33 people have been arrested across Moscow.
Officers in riot gear have moved into the capital and warned people not to protest.
Ms Sobol, a lawyer and video blogger, is one of the candidates excluded from the local elections. She has been on hunger strike for 21 days, and called on others to join the unsanctioned protest on Saturday.
Authorities said she is being held for violating regulations for street demonstrations.
In July, Ms Sobol was dragged out of the electoral commission office on a sofa.
Speaking to independent broadcaster Dozhd before her detention, she said the authorities “are doing everything they can to try to intimidate the opposition”.
“That is why it is important to come out today to show that Muscovites are not afraid of provocation and they are ready to continue to stand up for their rights,” she added.
What are the protests about?
Authorities detained more than 1,000 demonstrators last month during a demonstration, one of the biggest crackdowns in years.
Election authorities have barred opposition candidates from taking part in Moscow city authority elections planned for 8 September.
Officials said many of the signatures required for their candidacy applications were invalid. But protesters say they were excluded for political reasons.
Despite the recent arrests and a ban on further rallies, demonstrators are expected to take to the streets of Moscow again on Saturday.
What’s been happening in Moscow?
Authorities have launched an investigation into the protests.
On Friday, they detained a number of men – including Alexey Minyaylo, an independent politician and aide to Ms Sobol – in connection with the “mass unrest”, a charge which carries a sentence of up to 15 years in jail.
Prominent Kremlin critic Alexei Navalny has also been arrested in connection with the rallies.
He fell ill in jail with a swollen face and rashes over his body, and was briefly hospitalised.
Doctors said he had had an extreme allergic reaction, but Mr Navalny and his personal doctor said he may have been poisoned.