A Russian judge has ordered opposition leader Alexei Navalny jailed for 30 days after the leading Kremlin critic returned to Russia from Germany where he was recovering from nerve agent poisoning he blamed on President Vladimir Putin’s government.

The ruling followed a hastily set up court hearing at a police precinct where Mr Navalny was being held since his arrest at a Moscow airport on Sunday evening, which sparked sharp reactions at home and around the world.

A crowd of Navalny supporters outside the precinct shouted “Shame!” as the judge announced the ruling and Mr Navalny’s allies immediately called for protests. His arrest had already prompted a wave of criticism from US and European officials, adding to tensions between Russia and the West.

His top strategist, Leonid Volkov, announced preparations for “large rallies” on Saturday “all across the country”.

“Don’t be afraid, take to the streets,” Mr Navalny said in a video statement released after the ruling was announced. “Don’t come out for me, come out for yourselves and your future.”

At least 13 protesters were detained on Monday outside the police precinct where the court hearing was held, and at least 55 were rounded up by police in St Petersburg, Russia’s second-largest city, according to activists.

Navalny, 44, Mr Putin’s most well-known critic, campaigned to challenge him in the 2018 presidential election but was barred from running. He has issued scores of damning reports over the years about corruption in Russia under Mr Putin’s regime.

After recuperating for months in Berlin following his August 20 poisoning, he returned to Russia on Sunday evening despite the warrant for his arrest.

As expected, he was detained at passport control at Sheremetyevo Airport after the plane was diverted from landing at another Moscow airport in what was seen as an attempt to foil supporters who had gathered to cheer their hero’s arrival.

Russia’s prison service said Mr Navalny had violated probation terms from a suspended sentence on a 2014 money-laundering conviction, which he says was contrived and politically motivated. The service said it would seek to have him serve his three and a half-year sentence behind bars.

Mr Navalny described the move as an attempt by the Kremlin to deter him from coming back to Russia to continue his political activities.

A court hearing on the prison service’s motion to have him serve his suspended sentence in prison is scheduled for February 2, according to his lawyers.

Amnesty International called Mr Navalny a prisoner of conscience, and denounced the court hearing as a “mockery of justice”.

Calls for his immediate release came from European Commission president Ursula von der Leyen, the office of the UN High Commissioner for Human Rights, UK Foreign Secretary Dominic Raab and senior officials of other EU nations.

German government spokesman Steffen Seibert said “the Russian authorities have arrested the victim of an attempted assassination with a chemical weapon, not the perpetrator” and called for Mr Navalny’s release.

US president-elect Joe Biden’s pick for national security adviser, Jake Sullivan, called on Russian authorities to free Mr Navalny, and the outgoing secretary of state, Mike Pompeo, said the US “strongly condemns” the decision to arrest the opposition leader.

Russian Foreign Minister Sergey Lavrov said the stream of Western reactions to Mr Navalny’s arrest reflected an attempt “to divert attention from the deep crisis of the liberal model of development”.

“Navalny’s case has received a foreign policy dimension artificially and without any foundation,” Mr Lavrov said, arguing that the detention was a prerogative of Russian law enforcement agencies. “It’s a matter of observing the law.”

Mr Navalny spent the night at the police precinct outside Moscow. The court hearing on Monday was held at the precinct, and his lawyers said they were notified only minutes before.

“It is impossible, what is happening over here,” Mr Navalny said in a video from the improvised courtroom that was posted on his page in the messaging app Telegram. “It is lawlessness of the highest degree.”

The judge ordered that Mr Navalny be remanded in custody until February 15. His lawyers said they would appeal against the ruling.

Mr Navalny fell into a coma on a domestic flight from Siberia to Moscow on August 20. He was transferred from Siberia to a Berlin hospital two days later.

Labs in Germany, France and Sweden, and tests by the Organisation for the Prohibition of Chemical Weapons, established that he was exposed to a Soviet-era Novichok nerve agent.

Russian authorities insisted that the doctors who treated Mr Navalny in Siberia before he was airlifted to Germany found no traces of poison.

Moscow refused to open a full criminal inquiry, citing a lack of evidence that Mr Navalny was poisoned, and Russian officials have challenged Germany to provide proof of the poisoning.