Russian opposition leader Alexei Navalny told CBS News there’s a 50 percent chance he'll be killed for speaking out against Russian President Vladimir Putin.

Navalny, 41, organized two of the largest nationwide protests in Russia this year, and served a 25-day sentence for staging June's protest. He rose to prominence with his investigations of official corruption and has declared his intention to run for president against Putin in the 2018 election.

CBS News spent a week with Navalny in Russia before he was arrested in June, and the news outlet captured video of thousands of people protesting against government corruption, including many who held signs that read "Navalny 2018" and chanting "Putin is a crook."

Alexei and brother Oleg were found guilty in 2014 of embezzling Yves Rocher funds and Oleg was sentenced to three-and-a-half years in jail while Alexei received a suspended sentence, with many of his supporters claiming the charges were politically motivated. Alexei told CBS News he feels responsible for Oleg’s imprisonment.

"Well, it's 100 percent he's in jail just because he's my brother. It's the only reason," said Alexei.

Alexei has been protesting against Putin and government corruption since 2012. 

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