Russia's election commission has rejected anti-war challenger Boris Nadezhdin as a candidate in next month's presidential vote.

Nadezhdin has been relatively critical of Vladimir Putin's full-scale war in Ukraine when few dissenting voices have been tolerated in Russia.

Election authorities claimed more than 15% of the signatures he submitted with his candidate application were flawed.

He had tried to challenge this, but the commission rejected his bid.

Refusing to give up, Nadezhdin, 60, said on social media that he would challenge the decision in Russia's Supreme Court.

The Central Election Commission said that of the 105,000 signatures submitted by Nadezhdin, more than 9,000 were invalid and they cited a variety of violations.

That left 95,587 names, meaning he was just short of the 100,000 required signatures to register as a candidate, commission member Andrei Shutov said.

"There are tens of millions of people here who were going to vote for me, " Nadezhdin complained to the commission. "According to all polls, I am in second place after Putin."

"The decision has been made," declared commission chairwoman Ella Pamfilova. "If Nadezhdin wants, he can go to court," Tass news agency quoted her as saying.

Russia's presidential election is due to take place from 15-17 March, although the result is not in doubt as only candidates viewed as acceptable to the Kremlin are running.

A final decision on who can take part in the election will come on Saturday, but the election commission chairwoman said it was already clear there would be four candidates on the ballot.

Other than Vladimir Putin, they include nationalist leader Leonid Slutsky, parliament deputy speaker Vladislav Davankov and Communist Nikolai Kharitonov. All their parties have broadly backed Kremlin policies and none of the trio is seen as a genuine challenger.

"Running for president in 2024 is the most important political decision of my life. I am not retreating from my intentions," Nadezhdin wrote on Telegram. "I collected more than 200,000 signatures across Russia. We conducted the collection openly and honestly."

Boris Nadezhdin is one of the few government critics whose voices have been heard on the ubiquitous talk shows on state-run TV since the invasion on 24 February 2022. He has appeared as a type of anti-war "whipping boy" that other guests would target for criticism.