Jailed Russian opposition politician Aleksei Navalny says he has been officially informed by investigators that a new probe has been launched against him.

Navalny tweeted on October 20 that the probe was launched on charges of propagating terrorism, public calls for extremist activities, the financing of an extremist organization, and the rehabilitation of Nazism.

"[My] lawyers calculated that I may stay for up to 30 more years here [if convicted]," Navalny's tweet said, adding that the charges stemmed from the activities of his self-exiled associates' Popular Politics YouTube channel, which has criticized the Kremlin over Russia's ongoing unprovoked invasion of Ukraine.

Navalny has denounced the invasion, and earlier this month his organization said it would reopen its offices to fight against the Kremlin's mobilization.

"I am a genius of the underworld. Professor Moriarty is no match for me," he said sarcastically in a series of posts on Twitter, comparing himself to the nemesis of Sherlock Holmes.

"You all thought I had been isolated in prison for two years, but it turns out I was actively committing crimes," said Navalny, 46, who is able to post on Twitter through his lawyers and allies.

Navalny spokeswoman Kira Yarmysh said Popular Politics was launched by Navalny's allies after he had already been in prison for a year.

"Well, what can I say to you now? Subscribe to Popular Politics," said the last in the series of tweets.

There was no immediate official confirmation of the new case from the Investigative Committee.

The new charges against Navalny came on the same day that a court in Moscow ordered TV journalist Marina Ovsyannikova detained for just under two months, Russian state-run media reported. Ovsyannikova's lawyer said she and her daughter recently fled the country, so the court said the detention would begin upon her return.

It wasn't clear if she had any plans to return to Russia. Her lawyer, Dmitry Zakhvatov, said on October 17 that his client "had to leave Russia and is under the protection of a European state at the moment."

Ovsyannikova gained international recognition on March 14 when she burst onto the set of Channel One's Vremya news program holding a poster reading: "Stop the war. Don't believe propaganda. They are lying to you" in Russian. She also shouted: "Stop the war. No to war."

Ukraine-born Ovsyannikova was a producer with Channel One at the time of her protest. She was later detained and fined 30,000 rubles ($490) by a court for calling for illegal protests.

Navalny's Anti-Corruption Foundation (FBK) and other groups associated with the outspoken Kremlin critic, as well as his political movement, were declared "extremist organizations" by Russian authorities in June 2021 and disbanded.

Several of Navalny's associates have already been charged with the same offense.

Navalny was arrested in January last year upon his arrival to Moscow from Germany, where he was treated for a poison attack with what European labs defined as a Soviet-style nerve agent.

He was then handed a 2 1/2-year prison sentence for violating the terms of an earlier parole because of his convalescence abroad. The original conviction is widely regarded as a trumped-up, politically motivated case.

In March he was handed a nine-year prison term on charges of contempt and embezzlement through fraud that he and his supporters have repeatedly rejected as politically motivated.

With reporting by Reuters and AP