The widow of Russian opposition leader Alexei Navalny called on Wednesday for Russians to stage an election day protest against President Vladimir Putin by forming long queues outside voting stations.

Yulia Navalnaya has pledged to continue her husband's work and opposition to the Kremlin following his shock death last month in an Arctic prison colony.

In a YouTube video published Wednesday, Navalnaya backed an initiative to try to overload polling stations in this month's nationwide vote that will see Putin secure another six-year term as president.

"We need to use the election day to show that we are here, and we are many," Navalnaya said.

"We need to go to the polling station on one day at one time: 17 March at 12:00. What to do next? You can choose. You can vote for any candidate except Putin. You can spoil your ballot. You can write 'Navalny' in big letters," she said.

She called the upcoming presidential contest a "sham" and said Putin would "draw up any result he wants," but that a visual show of opposition on polling day could scare the Kremlin.

Navalny himself had also backed the proposal -- which organisers have called "midday against Putin" -- in one of his final posts from jail before he died.

Backers of the initiative hope it will be a legal and safe way for Russians to protest against the Kremlin.

Anti-government street rallies and demonstrations are effectively illegal in Russia, and organisers and participants can be sentenced to years in prison.

  'War, missiles and murders'  

Navalnaya also said she had taken hope from pictures of thousands streaming down the streets to visit Navalny's grave with flowers and tributes since his burial last Friday.

She, her two children and Navalny's brother all live abroad and did not attent the service, where they could have been arrested for their own opposition to Putin.

Calling her late husband's supporters the "bravest, most honest people in our country", she said the show of support proved there was significant opposition to the Kremlin inside Russia.

"We are many and we are strong," she said.

"These days I saw so much warmth, kindness and unity. It's exactly that which separates us from the people sitting in the Kremlin. They have a cult of the past, war, missiles and vile murders. And we have mutual love, support and faith in the future," she said.

Despite the Kremlin threatening to arrest mourners, long queues formed over the weekend outside the Borisovo cemetery in southern Moscow where Navalny was buried.

Supporters covered his grave in stacks of red, white and yellow carnations and roses.

  Arrests 

 Hundreds had been detained while laying flowers and placards at makeshift memorials to the opposition leader across Russia ahead of his official funeral.

Police in Moscow have since arrested at least five people who attended Navalny's burial or visited his grave, the OVD-Info rights group said, in a sign authorities could continue targeting Navalny supporters even after his death.

The former lawyer turned protest leader was Putin's most vocal critic for over a decade.

His exposes of alleged ill-gotten gains among Russia's political elite ignited anger towards the Kremlin and sparked huge demonstrations.

The Kremlin had outlawed his organisation as "extremist" and locked up several of Navalny's allies.

The Kremlin denies that Navalny had any significant support inside Russia and says Russian society is united behind Putin.

The former KGB agent, in power since the final day of 1999, is set to secure another six-year term in office in the March 15-17 vote.

Election authorities have barred genuine opposition candidates from the ballot, and Putin's most vocal critics are dead, in jail or exiled.

Kremlin spokesman Dmitry Peskov said Wednesday that Moscow "will no longer tolerate criticism of our democracy," as Western governments look set to condemn the upcoming poll as neither free nor fair.

"We will hold the kind of elections that our people need," he told reporters.