Russia's Supreme Court on Thursday rejected two legal challenges by anti-war candidate Boris Nadezhdin following his disqualification from next month's presidential election.
Announcing the court's judgement against him, Nadezhdin said would appeal against both decisions and file a further claim against the refusal of the electoral commission to register him.
"I don't give up and I won't give up," he said.
Nadezhdin had hoped to stand against President Vladimir Putin but was barred last week. The electoral commission said it found irregularities including names of dead people in the list of supporters' signatures he had presented in support of his candidacy.
By disqualifying him, the commission removed the only remaining candidate who had spoken out against what Putin calls his "special military operation" in Ukraine, describing it as a fatal mistake by the Kremlin leader. Another anti-war figure, Yekaterina Duntsova, had fallen at the first hurdle of the registration process in December.
While no one had expected Nadezhdin to win, he had run an efficient campaign and built up visible momentum by tapping into widespread unease about the war. People queued outside in the depths of winter to add their names to the list of at least 100,000 supporters' signatures he was required to submit.
"A huge number of people lined up in all cities of the country," he told the court. "There were no queues to sign up for other candidates. Only we had something like this."
Many commentators assumed Nadezhdin was only allowed to clear the initial hurdles to enter the election with the Kremlin's approval - something Nadezhdin denied - in order to give the appearance of competition.
The Kremlin says he was never a serious rival and that the election commission has simply applied the rules.
The outcome means that Putin, in power as president or prime minister since the last day of 1999, will face only three other candidates in the March 15-17 vote: Vladislav Davankov of the New People party; Leonid Slutsky, leader of the Kremlin-loyal ultra-nationalist Liberal Democratic Party; and Communist Party nominee Nikolai Kharitonov.
None are critical of Putin or pose any serious challenge.
Victory will extend Putin's rule by six more years, putting him on course to overtake Josef Stalin and become Russia's longest-serving ruler since 18th century Empress Catherine the Great.
Russia controls nearly a fifth of Ukraine's territory after nearly two years of war, with no end to the conflict in sight. But the costs to Moscow have been high, including heavy but undisclosed casualties, the emigration of hundreds of thousands of Russians, and frequent Ukrainian cross-border attacks on targets deep inside Russia.
The Kremlin says the West, by arming Ukraine, is fighting a proxy war against it, and that it will pursue the "special military operation" for as long as it takes.
Officials said at least six people were killed on Thursday in a Ukrainian rocket attack on Belgorod, a Russian city in a border region where missile and drone strikes have become part of daily life. There was no comment from Kyiv.
