Russian authorities have taken elaborate measures to curb protests against the jailing of opposition leader Alexei Navalny which have been planned for Saturday.

Mr Navalny’s associates in Moscow and other regions have been detained in the lead-up to the rallies in more than 60 Russian cities.

Opposition supporters and independent journalists have been approached by police officers with official warnings against protesting.

Universities and colleges in different Russian regions have urged students not to attend rallies, with some saying students may be subject to disciplinary action, including expulsion.

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Opposition leader Alexei Navalny, centre, signals to onlookers as he is escorted hand-cuffed after a court hearing in Moscow (Pavel Golovkin/AP)

Kremlin spokesman Dmitry Peskov said on Friday that “it is only natural that there are warnings … about the possible consequences related to noncompliance with the law” since there are calls for “unauthorised, unlawful events”.

Mr Navalny, an anti-corruption campaigner and the Kremlin’s fiercest critic, was arrested on Sunday when he returned to Russia from Germany, where he had spent nearly five months recovering from nerve-agent poisoning that he blames on the Kremlin.

On Monday, a judge ordered Mr Navalny to be jailed for 30 days.

He faces a years-long prison term, as authorities accused him of violating the terms of a suspended sentence in a 2014 conviction for financial misdeeds, including when he was convalescing in Germany.

Mr Navalny’s supporters have called for nationwide demonstrations on Saturday to pressure the government into releasing the politician but have come under pressure themselves.

On Thursday evening, police in Moscow detained three top associates of Mr Navalny. His spokeswoman Kira Yarmysh on Friday was ordered to spend nine days in jail, his close ally Lyubov Sobol was released on Thursday night and is facing a fine and Georgy Alburov is in detention awaiting court.

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Lyubov Sobol, a lawyer for Navalny’s Fund for Fighting Corruption, was among those arrested (Denis Kaminev/AP)

More than a dozen activists and Navalny allies in several Russian regions have been detained as well.

The Prosecutor General’s office and police have issued public warnings against attending or calling for unauthorised rallies.

The prosecutors have also demanded Roskomnadzor, Russia’s media and internet watchdog, to restrict access to websites containing calls to protest on Saturday.

On Friday, Russia’s largest social network VKontakte blocked all the pages dedicated to the rallies.

Roskomnadzor also announced that it would fine social media companies for encouraging children to participate in the protests.

The move came amid media reports of calls for demonstrations — and videos of school students replacing portraits of President Vladimir Putin in their classrooms with that of Mr Navalny — going viral among teenagers on social network TikTok.

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Police officers detain a supporter of opposition leader Alexei Navalny during a rally in St Petersburg (Dmitri Lovetsky/AP)

Russia’s Education Ministry has issued a statement urging parents to “shield” their children from the events on Saturday, stating that “no one has the right to drag young people into various political actions and provocations”.

Mr Navalny’s allies told supporters not to be discouraged and show up on Saturday.

“Don’t be afraid. Leave it to the Kremlin. We’re in the right, and we’re the majority,” Ms Sobol wrote in a Facebook post.

Dozens of influential Russians, including actors, musicians, journalists, writers, athletes and popular bloggers, have come out with statements in support of Mr Navalny, and some promised have to attend the demonstrations.