Russia appears to have detained an ally of Kremlin critic Alexei Navalny.
A lawyer for Lyubov Sobol says she was held for 48 hours after questioning.
He says they took her from her flat and seized a laptop.
Russian authorities confirmed Friday (December 25) that they had launched a criminal case, but made no mention of detention.
Sobol faces accusations of violently entering a flat that her supporters say is linked to a secret agent involved in a plot to kill Navalny.
The offence can carry a jail term of up to two years.
Navalny was the target of a poisoning he blames on Russia’s FSB security service.
The FSB denies his account of the incident.
But the move against Sobol is the latest in a clampdown on political opposition ahead of next year’s parliamentary election.
She is planning to run for office, though outspoken Kremlin critics are often prevented from standing.
Writing on Twitter, Navalny said authorities intended Sobol’s arrest as a warning not to look into his poisoning.