(Recasts with brother's detention)
By Anton Zverev and Maxim Shemetov
MOSCOW, Jan 27 (Reuters) - Police in Moscow detained Oleg Navalny, the brother of jailed Kremlin critic Alexei Navalny, on Wednesday during simultaneous searches of properties linked to the opposition politician, his allies said.
Tens of thousands of people took to the streets on Saturday to demand that the Kremlin release Alexei Navalny from jail, where he is serving a 30-day stint for alleged parole violations, which he denies.
Police had said the protests were illegal and detained close to 4,000 people. Navalny's allies plan to hold other rallies this Sunday.
Ivan Zhdanov, director of Navalny's Anti-Corruption Foundation, tweeted that Oleg had been in his brother's apartment as it was being searched. It was not clear why he had been detained.
Oleg Navalny was released from prison in 2018 after serving three-and-a-half years for an embezzlement conviction that Navany's suppporters say was designed to put pressure on Alexei and smother dissent. Alexei was given a suspended sentence in the same case.
Zhdanov said police appeared to be conducting the searches as part of an investigation into calls to hold protests, which breached restrictions imposed because of the COVID-19 pandemic.
"A lot of 'heavies' in masks. They started breaking down the door," he tweeted.
Zhdanov also posted video taken at another location showing Yulia Navalnaya, Alexei's wife, telling police to wait for her lawyer to arrive as they banged loudly at the door.
Navalnaya's lawyer, Veronika Polyakova, was allowed inside the apartment by police after standing outside the door for several hours.
"It used to be that touching the family was against the code of honour," Polyakova tweeted. "Now there is neither code, nor honour."
Police also searched the offices of the Anti-Corruption Foundation, his allies said. Photos on social media showed around 20 masked men waiting to gain entry.
Navalny has not yet returned to his home since being poisoned and almost killed in Russia last summer. Last week he was arrested at the airport as he returned to Moscow from Germany, where was treated and recovered. (Reporting by Anton Zverev, Alexander Marrow and Maxim Shemetov; Writing by Tom Balmforth and Gabrielle Tétrault-Farber; Editing by Kevin Liffey)