Roman Rubanov, a Navalny supporter, wrote on social media that the police said they were looking into reports that there was a bomb in the office, something he said came as a surprise to him.
Hundreds of supporters of Navalny began a nationwide day of protests against the authorities on Sunday, calling on voters to boycott what they said was a rigged presidential election on March 18. (Reporting by Andrew Osborn and Denis Pinchuk; Editing by Katya Golubkova)