Navalny transferred to prison after hunger strike: allies
Navalny was jailed for two and a half years in February on old embezzlement charges he and his supporters say are politically motivated.
He was sentenced shortly after returning to Russia from Germany, where he was receiving treatment for a near-fatal poisoning attack with a nerve agent.
President Vladimir Putin's most outspoken domestic critic declared a hunger strike in March to demand proper medical treatment for a growing list of health complaints, including back pain and numbness in his limbs.
The opposition politician called off the strike 24 days later.
The prison is located in the town of Pokrov 100 kilometres (60 miles) east of Moscow.
A court in Moscow is considering whether to designate Navalny's political network as an "extremist" organisation, which would remove potential challengers to the ruling United Russia party ahead of parliamentary elections in September.
A decision is expected as early as this week.
Last Friday, Putin approved an anti-extremism law expected to be used to ban his allies from running in elections. The Kremlin chief signed off on the legislation the day Navalny marked his 45th birthday behind bars.
Many of his close allies are either outside Russia or under arrest.
On Sunday, prominent Kremlin critic and former opposition lawmaker Dmitry Gudkov said he had left Russia for Ukraine due to pressure from authorities ahead of the elections.
Citing sources close to the Kremlin, Gudkov, 41, said that if he did not leave he would be arrested over a "fake" criminal case against him.