By Andrew Osborn

LONDON (Reuters) - Yulia Navalnaya, the wife of late Russian opposition leader Alexei Navalny, asked his supporters on Thursday to design "a people's gravestone" for him as a symbol of his political struggle against the Kremlin.

Navalny, whose death in February aged 47 in a prison above the Arctic Circle deprived the opposition of its most determined and charismatic leader, is buried in a Moscow cemetery where supporters come to pay respects.

In a YouTube video, Navalnaya said she and other family members were holding a competition to design his gravestone and invited supporters to submit ideas before the end of January.

She and the family would choose their three favourites and then allow supporters to vote on which one they liked best before announcing the result on Feb. 16, the first anniversary of Navalny's death.

"And let it be not just a monument, but a symbol. For some, a symbol of hope. For some, a symbol of strength and struggle. For some, a symbol of what we've been through together. And a symbol of how expensive freedom is.

"This monument is a way of saying that we have not forgotten Alexei and his ideas. And we will never forget."

Navalnaya, who was appointed chair of the U.S.-based Human Rights Foundation earlier this year, told the BBC broadcaster in October she planned to one day return to Russia and run for president when President Vladimir Putin is no longer in power.

Putin, 72, was re-elected in March for another six-year term.

ARREST THREAT

Navalny's political movement, the Anti-Corruption Foundation, is outlawed as "extremist" in Russia, where authorities portray it as a Western-backed project out to destabilise the country.

Navalnaya herself is accused of involvement in an extremist group and would face arrest if she returned to Russia.

Since Navalny's death, no single leader has emerged to unite the disparate opposition and there has been significant infighting between different Russian dissident groups abroad.

Navalnaya has accused Russian authorities of covering up the circumstances of her husband's death and Putin of having him killed, allegations the Kremlin has repeatedly dismissed as false.

U.S. intelligence agencies have determined that Putin did not order Navalny killed, according to the AP news agency and the Wall Street Journal newspaper.

Navalnaya said she hoped to one day be able to visit her husband's grave. "Let's create a true people's memorial for Alexei Navalny so that one day we can gather around it together," she said.