By Andrew Osborn and Gabrielle Tétrault-Farber
MOSCOW (Reuters) - Alexei Navalny, President Vladimir Putin's most prominent critic who was jailed at the weekend, on Tuesday released a video in which he and his allies alleged that an opulent palace belonged to the Russian leader, a claim the Kremlin denied.
The allegations, which first surfaced in 2010 when a businessman wrote about them to then-President Dmitry Medvedev complaining of official graft, come as Navalny's supporters urge people to join nationwide protests on Saturday.
Reuters reported in 2014 that the estate in southern Russia had been partly funded by taxpayer money from a $1 billion hospital project. A spokesman for Putin at the time did not respond to questions about Reuters' findings.
Navalny and his anti-corruption foundation published what they said were previously unseen photographs and detailed 3-D visualisations based on floor plans of the lavish interior along with a paper trail they said proved the 100 billion-rouble ($1.36 billion) Black Sea palace ultimately belonged to Putin.
Reuters could not independently verify their authenticity.
Kremlin spokesman Dmitry Peskov said the palace allegations were old and untrue.
"I'm not familiar with this investigation," Peskov was cited as saying by the Interfax News Agency. "However, I can immediately say that this is an old record. We explained many years ago that Putin does not have any palace in Gelendzhik (in southern Russia)."
The video, which has attracted more than 3 million views on YouTube, showed the palace contained a casino, theatre, ornate Tsarist-style interiors and an underground ice rink.
Navalny and his allies have released several investigations into alleged official corruption, using them to try to increase support for the opposition politician and his movement.
Navalny is being held in pre-trial detention for alleged parole violations after returning from Russia on Sunday for the first time since being poisoned last summer.
A Facebook events page for the planned protest in Moscow suggested around 2,000 people planned to go.
Navalny said in the video that it was time for Russians to force a change in leadership.
"Stop waiting and spending our lives and our taxes on the enrichment of these people," he said. "Don't be silent!"
Navalny faces four legal cases, all of which he says are politically motivated, that could see him jailed for years if found guilty.
A court in Moscow is due to hear one of them on Wednesday - allegations that he defamed a World War Two veteran, a crime punishable by up to five years in prison.
Peskov told reporters earlier on Tuesday that the Kremlin regarded Navalny's protest calls as alarming, but said it did not fear mass demonstrations. Mass gatherings are banned in Moscow during the coronavirus pandemic.
Peskov said the authorities would not be influenced by foreign countries calling for sanctions against Russia over its treatment of Navalny.
"This is an absolutely domestic matter and we will not allow anyone to interfere in it," he said.
($1 = 73.6859 roubles)
(Editing by Mike Collett-White)