The ruling concluded an hours-long court hearing set up at a police precinct where the opposition politician was detained after his arrest upon arrival in Moscow.
There are increasing concerns that Russian authorities will take advantage of lockdown measures.
More than 200 people showed up outside the headquarters of the FSB security services carrying placards and moving in single file as required by authorities for unauthorised demonstrations.
Twelve of the 24 Ukrainian servicemen captured on Sunday were sentenced to months in custody while another 9 will be jailed for two months, an order Kiev calls "illegal."
The Russian court also handed down jail terms ranging from 11 to 19 years to his four accomplices for organising the contract killing of the opposition leader Boris Nemtsov.
Alexei Navalny, a strong critic of Putin and Medvedev, called Russians to the streets to protest alleged government corruption. Around 1,700 of them ended up being detained.
The decision will complicate Alexei Navalny's plans to run for president against Vladimir Putin in 2018. Navalny says he will appeal the sentence and take part in the race regardless.
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