Alexander Lebedev suggested that the ruling was politically motivated
A Russian court has disqualified the billionaire owner of London's Evening Standard newspaper, Alexander Lebedev, from standing for mayor of Sochi.
Mr Lebedev had planned to stand against Anatoly Pakhomov, the acting mayor and member of PM Vladimir Putin's United Russia Party, in the 26 April election.
But a judge said the local election committee had acted "illegally" when it allowed the ex-KGB agent to register.
A spokesman for Mr Lebedev said the judgement was "absolute nonsense".
The election committee also condemned the decision, insisting it had correctly approved his application along with eight other candidates.
"This raises serious questions about the legitimacy of the election here in Sochi. The judge's decision is absolutely without precedent. We don't agree with it," Sergei Mendeleev, a commission member, told Britain's Guardian newspaper.
"As far as we are concerned he's still a candidate."
Correspondents say this month's mayoral election in the Black Sea resort of Sochi has attracted the attention of several high-profile individuals, as whoever takes up the post will have to prepare the city for the 2014 Winter Olympics.
Before the field of hopefuls was reduced from 26 to nine this month, it included a porn star, a former Bolshoi ballerina and Andrei Lugovoi, the prime suspect in the murder of Kremlin critic Alexander Litvinenko.
Sochi's new mayor will have to prepare the city for the 2014 Winter Olympics
Mr Lebedev part-owns the Russian newspaper Novaya Gazeta, which prides itself on its independence from the government, and is believed to be Russia's 39th richest man with an estimated net worth of $3.1bn (£2.1bn).
He was on the shortlist along with Mr Pakhomov and Boris Nemtsov, a prominent Kremlin critic.
But on Monday, a court in Sochi said Mr Lebedev's registration was invalid because he had failed to submit a financial document.
Mr Lebedev's spokesman, Artyom Artyomov said the decision was "absolute nonsense and completely impossible to implement", and that he would continue to campaign as normal while he appealed.
"This is a desperate attempt to get rid of the only serious challenger and it's completely illegal. After this publicity, I am certain that Lebedev will become mayor," he said.
On his blog, Mr Lebedev suggested the judge's decision had been politically motivated.
"It's a common trick to take out a strong candidate," he wrote, adding that similar tactics had been used ahead of previous votes.
Mr Nemtsov said the court decision was part of a government push to ensure victory for the acting mayor, Mr Pakhomov.
"They have been given the task of pushing this candidate through at any price," he told a news conference.