(CNN) -- Russian opposition leader Alexei Navalny, facing a five-year prison term and free pending an appeal, returned to Moscow on Saturday and vowed he will be elected mayor.
Hundreds of supporters and journalists met Navalny's train as he returned from his trial in Kirov, according to state-run Ria Novosti.
"We are a huge, powerful force," Navalny told the crowd. "I'm very glad that we've started to recognize that force ourselves. ... I want to apologize to you for not believing so strongly in you."
His apology referred to his statements Friday that he was not certain he would run for mayor. By Saturday, he was declaring, "We will go to the elections and we will win," Rio Novosti reported.
Navalny was detained overnight Thursday after a court in Kirov city found him guilty of misappropriating about $500,000 in a lumber deal when he was an adviser to the region's governor. He was released Friday.
Navalny denied wrongdoing and said he was targeted because he is one of Russian President Vladimir Putin's most outspoken critics.
'A parody of a prosecution'
Navalny's conviction and sentencing Thursday prompted wide condemnation.
The European Union's top diplomat, Catherine Ashton, called the trial a sham. And former Soviet leader Mikhail Gorbachev issued a statement saying the case "unfortunately confirms that we do not have an independent judiciary."
Navalny has been a prominent organizer of street protests, and has attacked corruption in Russian government.
"Navalny's prosecution is meant to silence a leader and messenger," said Rachel Denber, deputy director of Human Rights Watch's Europe division
Amnesty International's Europe and Central Asia program director, John Dalhuisen, said, "This was a parody of a prosecution and a parody of a trial. The case was twice closed for lack of evidence of a crime, before being reopened on the personal instruction of Russia's top investigator."