Russian opposition politician and anticorruption campaigner Aleksei Navalny has been detained outside his residence in Moscow, his spokeswoman Kira Yarmysh said on Twitter on August 25.
Yarmysh said Navalny had been taken to a local police station and that his cell phone was taken away by the police.
She said later that his detention appears to be connected to January 28 protests supporting a boycott of Russia's presidential election.
More than 250 people, including Navalny, were detained across the country during those protests.
Yarmysh said in a tweet later on August 25 that Navalny was taken from the Moscow police precinct where he was held due to a suspected injury to his finger that he may have suffered as he was being detained.
Navalny, 42, has served several jail terms on charges related to organizing antigovernment protests, and he was convicted twice on financial-crimes charges he says were trumped up by the Kremlin as retribution for his opposition to Russian President Vladimir Putin.
He was barred from running in the March 18 presidential election because of his criminal record.
Earlier on August 25, Navalny announced on Twitter that he and his team planned to make several "very cool announcements" via his YouTube channel and urged people to tune in.
The YouTube link attached to the tweet said the video was unavailable.
Navalny is currently planning protests to be held in several Russian cities on September 9 against a controversial government plan to raise the retirement age.
The plan sparked widespread anger after it was announced last month, and Putin's approval ratings have fallen.
Tens of thousands of people protested in cities across the country on July 28, and many other demonstrations have been held.
A top security official at the Moscow mayor's office said on August 25 that city authorities were considering an application filed by Navalny's supporters to stage the protest in the Russian capital on September 9, the same day that the Moscow mayoral election will be held.
Navalny's supporters are seeking permission to hold the protest on a central Moscow street near the Kremlin.
Moscow authorities frequently reject opposition activists' requests to stage rallies in the city center, citing security concerns and disruptions for road traffic and pedestrians.