Russian authorities have barred a coalition co-led by top opposition activist Aleksei Navalny from participating in a major regional poll, the party says on its website.

The election commission in the Siberian city of Novosibirsk barred the RPR-Parnas alliance from registering to run in regional polls, the July 24 statement said.

The coalition of two opposition parties is led by politician and lawyer Navalny and former Prime Minister Mikhail Kasyanov.

Novosibirsk's election commission claimed the signatures the party had gathered from supporters did not pass official authenticity checks.

The coalition said it was removed from the polls "for political reasons -- the authorities are afraid to let the opposition into the elections."

The group plans to go before the election commission to rebut the decision on July 27.

According to electoral rules, RPR-Parnas needed to gather more than 11,000 signatures from residents in order to participate in the elections for Novosibirsk's regional parliament.

The group claimed to have more than enough signatures to meet that test.

"Elections without the participation of the opposition (and the only independent opposition is RPR-Parnas) are not elections," Navalny wrote on Twitter.

He said the election commission should answer to the 17,000 people who supported his party's presence on the ballot.

"A huge number of inhabitants of the region want to vote for the democratic opposition," he said.

Elections for Novosibirsk's regional assembly are set for September 13. The city is Russia's third-largest, with more than 1.5 million residents. It lies around 2,800 kilometers east of Moscow.

In April, Russia took the party led by Navalny off the list of authorized parties, while the activist leader himself was taken to court.

Though he was spared prison time after a tense hearing in May, the charismatic opponent's supporters say the charges of fraud originated in the Kremlin rather than in court.

With reporting by AFP