An outspoken pro-war blogger who has fiercely criticised Russia's military strategy in Ukraine has said he wants to challenge Vladimir Putin in next March's presidential elections.

Igor Girkin, 52, led pro-Russia fighters in eastern Ukraine in 2014, following Moscow's annexation of the southern Crimea peninsula.

Girkin is in jail awaiting trial for extremism, which he denies.

He said he wanted to disrupt the "sham" poll with the winner already known.

This comment is widely seen in Russia as a reference to President Putin, who is yet to publicly declare that he will run again.

In a letter to supporters published on Telegram on Sunday, Girkin, whose nom de guerre is Strelkov, 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 hoped 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, even though he knew he would not be allowed to stand.

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 in February 2022, 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.

President Putin's spokesman Dmitry Peskov said in an interview published on Friday that he hoped his boss would stand for another term.

He first served as president from 2000 to 2008, returning to the role from a stint as prime minister in 2012. Recent amendments to the Russian constitution allow him to stay in power until at least 2036 if he is elected again.