Supporters of Russian opposition leader Alexei Navalny have endorsed him for the presidency and are set to file his nomination with election authorities.

President Vladimir Putin's most formidable foe in all his 18 years in power, Navalny is barred from running, however, because of a criminal conviction in a case that has been viewed as politically motivated. He could run if he gets a special dispensation or if the conviction is canceled.

Some 800 Navalny supporters gathered for a formal meeting on Sunday to endorse him. The gathering's nomination is to be submitted later in the day to election authorities, who will rule whether he can run.

Navalny's yearlong grass-roots campaign has galvanized people in the most remote corners of Russia. Putin's 80 percent approval ratings, however, make him a certain winner in the March vote.