Imprisoned Russian opposition leader Alexei Navalny is in failing health because of a new suspected poisoning and is back in a punishment cell after a few days in regular confinement, a spokeswoman said Wednesday.

Anna Veduta, a Washington, DC-based vice president of Navalny`s Anti-Corruption Foundation, told The Associated Press the 46-year-old Navalny fell ill last Friday when he was let out of the punishment cell and put in a conventional cell. He had lost about 18 pounds over the past 15 days. On Monday, Navalny wrote on Twitter, he was put back in a punishment cell for another 15-day term.