Nobody expects Nadezhdin, 60, to win if he is allowed to run, given Putin's long dominance and control of the state. But Nadezhdin has become the preferred candidate of some Russians who oppose Moscow's war in Ukraine, something it calls a special military operation.

Nadezhdin needs the Central Election Commission to approve signatures he submitted on Wednesday from more than 100,000 supporters across Russia in order to get his name on the ballot for the March 15-17 election.

The electoral commission met on Friday and its deputy chairman, Nikolai Bulayev, said some of the supporter lists submitted by candidates contained the names of dead people.

Bulayev said that when officials detected the names of dozens of "people who are no longer on this earth", it raised questions about the honesty of the signature-collectors and the candidates themselves.

Nadezhdin has so far run an efficient campaign and surprised some analysts with his trenchant criticism of the war. He has said that Putin's decision to send his army into Ukraine was a "fatal mistake" and that he would would try to end the conflict through negotiations.

State news agency TASS said the results of the commission's checks on the signatures submitted by Nadezhdin and another candidate, Sergei Malinkovich, would be presented on Monday.

There was no immediate comment from Nadezhdin.

Some analysts believe his growing profile and anti-war stance are becoming an annoyance for Putin, 71, and that the Kremlin may seek a pretext to stop him. In the past, electoral authorities have disqualified candidates whose signatures from supporters were ruled as invalid.

The Kremlin has said it does not see Nadezhdin as a serious rival to Putin, who it says will win the election on the basis of overwhelming popular support built up during more than two decades in power as either president or prime minister.