Russian President Vladimir Putin on Monday dismissed claims by opposition leader Alexei Navalny that he owns a luxury property on the Black Sea worth $1.35 billion, as the opposition urged fresh nationwide demonstrations.

Courts around Russia started handing down short jail sentences to demonstrators arrested during nationwide opposition rallies last weekend, while the foreign ministry accused US diplomats of encouraging Russians to join the protests.

Navalny's aides urged his supporters to take to the streets again next Sunday ahead of a court case that could see Russia's most prominent Kremlin critic put behind bars for more than three years.

Security forces were patrolling on Monday after weekend protests saw thousands arrested
Security forces were patrolling on Monday after weekend protests saw thousands arrested AFP / Alexander NEMENOV

The 44-year-old campaigner was detained just over a week ago when he returned to Moscow from Germany, where he had been recuperating from exposure to a Soviet-designed toxin.

He called on his supporters in dozens of cities to rally last weekend and released a two-hour investigation into the palatial seaside property to spur allies to demonstrate.

The rallies saw a record number of arrests, and Putin on Monday denied having anything to do with the property in Navalny's video, which has now been watched 86 million times.

Timeline of the poisoning of Russian opposition campaigner Alexei Navalny to his arrest shortly after arrival at Moscow airport.
Timeline of the poisoning of Russian opposition campaigner Alexei Navalny to his arrest shortly after arrival at Moscow airport. AFP / Gal ROMA

"Nothing that is listed there as my property belongs to me or my close relatives, and never did," Putin said during a video call with Russian students.

Navalny's report -- his most-watched anti-corruption probe by far -- claims the property is worth $1.35 billion and features everything from an underground ice rink to a casino.

The video claiming Putin owns the palatial home on the Black Sea has drawn tens of millions of views
The video claiming Putin owns the palatial home on the Black Sea has drawn tens of millions of views AFP / Alexander NEMENOV

Leonid Volkov, a key aide to the Kremlin critic, urged Russians to take to the streets again on January 31 "for Navalny's freedom, for freedom for all, and for justice".

Saturday's rallies saw clashes between police and protesters, 3,700 of whom were detained according to the OVD-Info monitoring group.

Putin said on Monday that Russian citizens have the right to express themselves but that they must do so "within the framework of the law".

The weekend demonstrations were the biggest in Russia for years
The weekend demonstrations were the biggest in Russia for years AFP / Kirill KUDRYAVTSEV

According to OVD-Info, by Monday morning more than 80 people have been handed short-term jail sentences over the protests while at least 15 criminal probes have been launched.

Putin also said minors should not be encouraged to join the rallies, referring to a claim repeated by authorities that the opposition had encouraged young people to protest.

"That's what terrorists do. They put women and children in front of themselves," Putin said.

Political analyst Alexei Zakharov, who cited polls conducted at Moscow's rally, said on Facebook that demonstrators were on average 31-years-old, while only 10 percent of participants were 18 or younger.

The Russian foreign ministry on Monday repeated claims that US diplomats had encouraged Russians to participate in the rallies, and said it had lodged a "strong protest" with the American ambassador.

That allegation followed earlier claims by the Kremlin that the US embassy was interfering in Russian affairs by publishing protest routes ahead of the rallies.

An embassy spokeswoman told AFP that it was "routine practice" for diplomatic missions to issue safety messages to their citizens abroad.

Russian foreign ministry spokeswoman Maria Zakharova said Moscow would probe American tech companies over "interference" related to the demonstrations.

Ahead of the rallies, Russia's media watchdog Roskomnadzor ordered social media platforms including YouTube and Instagram to delete calls for demonstrations posted on their platforms.

Navalny's arrest was met with widespread condemnation in the West, with the European Union saying it was considering new sanctions on Russia -- although EU ministers decided at a meeting Monday that this was "premature", according to one European diplomat.

EU foreign policy chief Josep Borrell is due to visit Moscow early next month and indicated that he will press the Kremlin on Navalny's arrest.

Stephane Dujarric, spokesman for the United Nations Secretary-General, meanwhile said people should not be detained "solely for expressing their opinion", highlighting the "basic right" of freedom of expression and peaceful assembly.