Moscow (AFP) - A Russian opposition coalition co-led by leading Kremlin critic Alexei Navalny has had nearly all its candidates barred from September regional and local elections, a representative told AFP on Monday.

"We have been excluded from all the polls that we wanted to take part in," said Sergei Davidis of the RPR-Parnas opposition coalition, which includes the party of slain Kremlin critic Boris Nemtsov.

"This shows that the authorities are afraid of us. It shows we're hitting them in a sensitive spot," Davidis said.

Navalny, a key figure in mass opposition protests against President Vladimir Putin who has twice been given suspended sentences for fraud and spent a year under house arrest, accused the authorities on Friday of trying to rig the local and regional elections planned in 11 regions on September 13.

"If you are not cheaters, then why won't you let us take part in the elections?", he asked in a speech at the headquarters of the central electoral commission on Friday.

Russia's opposition has been marginalised under Putin and the coalition was planning to use its participation in the regional polls as a rehearsal for parliamentary elections next year.

"We are set on taking part in the national elections next year and view our campaign as successful, despite the obstacles we have faced," Davidis said.

In the latest blow for the opposition, electoral officials in the central Russian industrial city of Nizhny Novgorod on Monday refused to register its candidate for the September 13 vote.

The officials claimed that the signatures the bloc presented in support of the candidate were invalid, RPR-Parnas said.

The authorities have given various reasons for the coalition's exclusion, including its alleged collection of forged signatures.

The bloc's only representative in the September polls will be opposition activist Yegor Savin in the Siberian city of Novosibirsk, Russia's third most populous.

"It's a miracle that I was not excluded," Savin, who recently ended a 13-day hunger strike launched to protest against the opposition's registration difficulties, told AFP.

"We have to gain more supporters, even though we cannot take part in the polls," he said.

"We have to become so strong that they won't be able to bar us from elections so easily."