Jan. 27 (UPI) -- Police in Russia on Wednesday raided the home and offices of jailed opposition leader Alexei Navalny as well as those of his allies, some of whom have been detained, associates of the staunch critic of President Vladimir Putin said, as protesters plan to take to the streets for a second straight weekend in demand for his release.
The searches and arrests follow mass protests throughout Russia over the weekend in demand that the authorities release Navalny, 44, who was arrested earlier this month for allegedly violating the terms of a suspended 2014 prison sentence.
Navalny was detained after his plane touched down at Sheremetyevo airport on Jan. 17 on his return from a 5-month stay in Germany where he was receiving medical treatment for nerve-agent poisoning. Russia has denied being behind the assassination attempt.
In a crackdown on the protests on Saturday, police arrested at least 3,700 people, human rights group Amnesty International said, citing data from OVD-Info, a Russian human rights group that monitors such assemblies.
Ivan Zhdanov, the director of Navalny's Anti-Corruption Foundation known as the FBK, said police on Wednesday searched Navalny's Moscow apartment, arresting his brother, Oleg Navalny, who was inside.
"There are many 'heavy' ones wearing masks. They started to break down the door," he said. "In what case and on what basis we do not know."
Oleg has been detained at the Ministry of Internal Affairs, suggesting he is a suspect in a criminal case.
The offices of FBK were also searched, he said, tweeting security camera footage of some two dozen police in the corridor of the organization's office.
"How many cops does it take to conduct a search without people there," he asked.
The Twitter account of FBK said the search was due to "a violation of sanitary and epidemiological standards."
The apartment of Navalny's wife, Yulia Navalnaya, was also searched, Zhdanov tweeted.
Zhdanov said the searches were conducted by the Ministry of Internal Affairs under Article 236 of the criminal code, which a copy from the World Trade Organization states concerns the violation of "sanitary and epidemiological rules, which has resulted in, by negligence, mass diseases or poisoning of people."
Lyubov Sobol, lawyer for the FBK, and Anastasy Vasilyeva, head of the Alliance of Doctors and Navalny ally, were also detained.
"They detained me, almost broke down the door and issued a new search," Vasilyeva tweeted. "I'm not afraid of anything, I don't feel sorry for anything for the truth and the future of our children."
"Don't be afraid!" she said.
Video and pictures of Sobol in handcuffs escorted by police were tweeted from her Twitter account, stating she has been detained for 48 hours as a suspect in a criminal case.
Before her arrest, Sobol confirmed the searches of Navalnaya's home, adding that the apartments of Navalny spokeswoman Kira Yarmysh, FBK investigator Georgy Alburov and Vasilyeva had been raided as well as the offices of Navalny's YouTube channel.
"They can search us as much as they want, but we will not be afraid on them," Navalny's Anti-Corruption Foundation tweeted, encouraging people to protest in cities throughout Russia on Sunday for his release.