- But he said he hopes his attempt to unite patriotic forces would disrupt the Kremlin's plans for the polls in which "the only winner is known in advance".
- He told his supporters to set up a headquarters for his campaign, and to start collecting signatures for his candidacy,
An outspoken pro-war blogger who has fiercely criticised Russia's military strategy in Ukraine has said he wants to challenge Vladimir Putin in March's presidential elections.
Igor Girkin, also known as Igor Strelkov, played a key role in Russia's 2014 annexation of Crimea.
Girkin is in jail awaiting trial for extremism, which he denies.
He said knows he might not be allowed to take part, but he hoped to disrupt the "sham election".
In a letter to supporters published on Telegram, he said: "I understand perfectly well that in the current situation in Russia, participating in the presidential campaign is like sitting down at a table to play with card sharps."
But he said he hopes his attempt to unite patriotic forces would disrupt the Kremlin's plans for the polls in which "the only winner is known in advance".
"This is our chance to unite in the face of external and internal threats," he said.
He told his supporters to set up a headquarters for his campaign, and to start collecting signatures for his candidacy,
Supporters of Girkin told Reuters that his criminal investigation had been extended until 18 December, and that he could theoretically take part in the polls as he has not been convicted yet.
Girkin is a former FSB intelligence colonel. He was one of three men convicted in absentia by a Dutch court last November of murder for his role in the 2014 shooting down of a Malaysia Airlines passenger jet with the loss of all 298 people on board.
After Russia's full scale invasion of Ukraine he gained prominence by mocking Russian tactics and repeatedly warned that Russia faced revolution and even civil war unless President Putin's military top brass fight the war in Ukraine more effectively.
He was arrested in July. If convicted of extremism he could face up to five years in jail.
Russian authorities have cracked down on nationalist critics who have called for a much tougher approach to fighting the war in Ukraine, after the failed mutiny by Wagner chief Yevgeny Prigozhin in June.
Prigozhin was killed in August in a plane crash, the causes of which are still unclear.
Mr Putin has not publicly declared that he will run again, but Kremlin spokesman Dmitry Peskov said in an interview published on Friday that he hoped his boss would stand for another term as president.
He first served as president from 2000 to 2008, returning to the role from a stint as prime minister in 2012. He could stay in power until at least 2030 if he is elected again.