Alexei Navalny is unconscious and on a ventilator, his spokeswoman said on Thursday. The Russian opposition leader, center, is seen here during a rally in Moscow last year along with his wife, Yulia, right. The rally marked five years since the assassination of politician Boris Nemtsov.

Alexey Navalny, Russian opposition leader, center, and his wife Yulia, right, walk with demonstrators during a rally in Moscow, Russia, on Saturday, Feb. 29, 2019. The rally marked five years since the assassination of politician Boris Nemtsov. Photographer: Andrey Rudakov/Bloomberg via Getty Images