Russian opposition leader Alexei Navalny has returned to Moscow after his surprise release from prison, and says he will continue his campaign for mayor of the capital city.

He and his wife arrived Saturday on an overnight train from Kirov, and were met at the railway station by a crowd of cheering supporters. Navalny told the crowd that he will run in the September 8 mayoral election and would win.

In Kirov Thursday, Navalny was sentenced to five years in prison after a conviction of embezzling $500,000 worth of timber from a state-owned company, while working as an adviser to a provincial governor in 2009. But an appeals court surprisingly released him Friday while he appeals his sentence and runs for office.

Thousands of people in several Russian cities demonstrated against the conviction.

White House officials said Thursday the Obama administration was "deeply disappointed" by the ruling, which it called "the latest example of a disturbing trend aimed at suppressing dissent in civil society in Russia."

European Union foreign policy chief Catherine Ashton said she was concerned about Navalny's conviction and sentence, saying the charges had not been substantiated during the trial.

The 37-year-old opposition leader, who has exposed alleged government corruption, said the charges are politically motivated and intended to silence him.

Last year, Navalny angered President Vladimir Putin by leading mass street demonstrations in Russia's capital.

Navalny also helped organize mass protests starting in 2011 against alleged electoral fraud and Mr. Putin's return to the presidency.