Russian authorities raided Alexei Navalny's offices on Thursday, just a day after the Kremlin opponent said one of his allies had been forcibly conscripted and sent to serve at a remote Arctic base.
Navalny was taken from the office by officers of the federal court bailiffs' service that forced their way into the office. But the service later said he hadn't been detained.
Lyubov Sobol, an attorney with Navalny's foundation, said the officers claimed to be searching for evidence connected to a case against the foundation's director, Ivan Zhdanov.
A criminal case was opened against Zhdanov in August for failing to follow an order to remove a video version of a report claiming corruption by Medvedev.
Navalny released pictures and footage of the raid on his social media accounts.
In a separate incident, Ruslan Shaveddinov, a project manager at Navalny's anti-corruption foundation, went missing Monday after police broke into his Moscow flat and his phone's SIM card was disabled.
He resurfaced Tuesday at a secret air defence base on the remote Novaya Zemlya archipelago in the Arctic Ocean, Navalny said.
"He has been unlawfully deprived of freedom," Navalny -- President Vladimir Putin's top opponent -- said in a blog post, calling the 23-year-old a "political prisoner".
The Russian military insisted that Shaveddinov had been dodging the draft for a long time.
Russian men are eligible for conscription between the ages of 18 and 27 and serve one year's military service. However, many find ways to avoid this in a corrupt, flawed system.
Opposition supporters called for Shaveddinov's release, staging protests in Moscow including outside army headquarters,
One of the placards read: "Mandatory military service is a tool of repression."
"Happy New Year 1937," said another placard, referring to the peak year of Stalin-era purges. "Ruslan Shaveddinov has been kidnapped by the FSB (security service) and exiled to Novaya Zemlya," said the sign, according to photographs released by Navalny's allies.
Navalny said Shaveddinov has a medical condition that disqualifies him for military service but that he was forcibly drafted and sent to the Arctic base without basic training.
Vyacheslav Gimadi, a lawyer for Navalny's foundation, said Defence Minister Sergei Shoigu and commander-in-chief Putin were directly responsible for what he claimed was an act of "kidnapping".
Navalny's spokeswoman Kira Yarmysh, who is Shaveddinov's partner, said Shaveddinov had recently acted as a contact person for opposition lawmakers in Moscow city parliament.
"Perhaps this is the reason this has happened," Yarmysh told AFP.
She said Shaveddinov had managed to call her from Novaya Zemlya using other people's phones.
Navalny said Shaveddinov was not allowed to communicate with the outside world or use a phone, unlike other servicemen.
The military also assigned a man to follow Shaveddinov all the time, he added.
"The armed forces themselves don't know what the hell they should do with him," Navalny said.
Putin's spokesman Dmitry Peskov told reporters he did not know whether Shaveddinov had been dodging the draft.
"If he had and was drafted in this manner then everything was done in strict accordance with the law."
Melnikova, head of the Union of the Committees of Soldiers Mothers of Russia, accused officials of violating all possible conscription procedures in Shaveddinov's case.`
43-year-old Navalny helped organise major protests against the government this summer when tens of thousands took to the streets of Moscow to demand fair elections.
A number of people received jail terms for taking part in those protests.
Opposition supporters said the treatment of Shaveddinov was a new low in Moscow's fight against dissenters.