Russia's leading Kremlin critic, Alexey Navalny, was detained by police in the outskirts of Moscow on Sunday, moments after his return to the country and five months after he was poisoned with the nerve agent Novichok.

Live footage from Russian broadcaster TV Rain showed him talking with dark-uniformed and masked officers at Moscow's Sheremetyevo airport, then kissing his wife Yulia before walking away with them.

The couple were returning from a five-month stay in Germany, where he had been recovering from the Novichok poisoning. They landed at Sheremetyevo just after 8 p.m. local time (12 p.m. ET), according to flight data information.

“This is the best day in the past five months,” Navalny told journalists at the airport just before his arrest.

“Everyone is asking me if I'm scared. I am not afraid,” he said. “I feel completely fine walking towards the border control. I know that I will leave and go home because I'm right and all the criminal cases against me are fabricated.”

Navalny was placed on the country's federal wanted list last month for violating terms of probation related to a years-old fraud case, which he dismisses as politically motivated.

A statement on Sunday from the Federal Penitentiary Service (FSIN) confirmed Navalny had been detained, and said he would remain in custody until a court hearing later this month, according to TASS.

He is being held at a police station in the city of Khimki, just north of Central Moscow, and has not been allowed access to his lawyer, according to Navalny's spokesperson Kira Yarmysh and regional coordinator Leonid Volkov.

Navalny has been a perennial thorn in Russian President Vladimir Putin's side, raising concerns for his safety in the country.

A joint investigation by CNN and the group Bellingcat implicated the Russian Security Service (FSB) in Navalny's August poisoning, piecing together how an elite unit at the agency followed Navalny's team throughout a trip to Siberia, when Navalny fell ill from exposure to military-grade Novichok.

The investigation also found that this unit, which included chemical weapons experts, had followed Navalny on more than 30 trips to and from Moscow since 2017. Russia denies involvement in Navalny's poisoning. Putin himself said in December that if Russian security services had wanted to kill Navalny, they “would have finished” the job.

Nevertheless, several Western officials and Navalny himself have openly blamed the Kremlin.

Flight diverted to Sheremetyevo

Navalny's flight from Berlin on Russian carrier Pobeda was originally scheduled to land at Vnukovo airport, where a crowd of hundreds of supporters and journalists waited to greet him.

Videos by independent media outlets Novaya Gazet and Media Zona showed police arresting several allies waiting at Vnukovo amid temperatures of around -20 degrees Celsius (-4 degrees F), including politician and lawyer Lyubov Sobol and Ruslan Shaveddinov, who works for Navalny's Anti-Corruption Foundation.

The flight was diverted at the last minute to Sheremetyevo. According to the Vnukovo press office, the flight was redirected due to an “emergency situation” in which two runways were blocked by equipment that had been stuck in the snow, Russian media group RBC reported.

But Navalny blamed the change of destination on the Russian government, apologizing to his fellow passengers upon landing. “I would like to apologize to the passengers on this flight. As I understand, hundreds of people suffered because Vnukovo was closed, thousands of people apparently got stuck simply because the road to Vnukovo had been blocked, here traffic was restricted.”
He added: “They are jeopardizing the air safety of a wonderful big city. Why? Just so Putin could say: “Who needs him?!”

After he was taken into custody, his wife Yulia Navalny told reporters, “They are so afraid of [Navalny], they paralyzed all flights in Moscow tonight, so many people were let down over a man who simply flew back to his homeland.”

“The most important thing is what Alexey said today,” she added. “He is not afraid, I am not afraid, and I urge you all not to be afraid either.”

European leaders and diplomats reacted quickly to news of Navalny's detention, with European Parliament President David Sassoli and European Council President Charles Michel among the many calling for Russian authorities to release him.

“The detainment of Alexey Navalny upon arrival in Moscow is unacceptable. I call on Russian authorities to immediately release him,” tweeted Michel.

Navalny's arrest “is an offence to the international community, to Europe that helped save his life. We ask the Russian authorities for his immediate release,” tweeted Sassoli. “We are ready to invite him to the European Parliament.”

The Austrian Ministry of Foreign Affairs tweeted that it was “deeply concerned” about Navalny's detention, adding: “A vibrant civil society and political opposition are cornerstones of all democratic societies. Austria calls for his immediate release and a full & independent investigation into the attack on his life.”

Josep Borrell, High Representative of the European Union for Foreign Affairs and Security Policy, called for Navalny's immediate release in a tweet, saying that “Politicisation of the judiciary is unacceptable.”

In the US, members of both the incoming and outgoing presidential administrations voiced support for Navalny. “The Kremlin's attacks on Mr. Navalny are not just a violation of human rights, but an affront to the Russian people who want their voices heard,” tweeted Jake Sullivan, National Security Adviser for the incoming Biden administration.

US Secretary of State Mike Pompeo also issued a statement condemning the detention. “We note with grave concern that his detention is the latest in a series of attempts to silence Navalny and other opposition figures and independent voices who are critical of Russian authorities,” he said.

What's next for Navalny?

Navalny and his Anti-Corruption Foundation have been the subjects of a number of legal cases, which he and allies believe are politically motivated.

In 2014, Navalny was found guilty of fraud after he and his brother Oleg were accused of embezzling 30 million rubles ($540,000) from a Russian subsidiary of French cosmetics company Yves Rocher. While Navalny was given a suspended sentence, his brother was jailed.

On December 28, FSIN accused Navalny of violating the terms of his probation by failing to show up for scheduled inspections while in Germany and requested that a court replace his suspended sentence with a real prison term.

Yarmysh, his spokeswoman, said the claim was unreasonable. “The Penitentiary Service –knowing full well that Navalny is being treated in Germany — is trying to jump on the last train (Alexey's probation period ends on December 30!) and demands that he reports for inspection tomorrow!” she tweeted.

A hearing has been scheduled for January 29. If the FSIN request is granted, Navalny will likely be jailed for 3.5 years, according to the court's press service as reported by RAPSI.

If Navalny is not convicted later in January, he will still face an investigation for a newer fraud case, in which he and his Anti-Corruption Foundation have been accused of misusing donations from supporters.

In a video address posted on his Instagram last month, Navalny called the new criminal cases brought up against him in Russia “demonstratively fabricated” and an attempt to prevent him from coming back to Russia.

“The situation with Navalny looks like two trains running towards each other at full speed, bound to collide,” said Tatiana Stanovaya, a non-resident scholar at the Carnegie Moscow Center. “There will be many victims.”

Attacks on Navalny's allies have indeed continued. Pavel Zelensky, a cameraman with Navalny's Anti-Corruption Foundation, was arrested Friday and will be detained until the end of February. His lawyer has not commented on the case.

According to Agora, a Russian human rights organization, Zelensky was accused of extremism for tweets from September, in which he blamed the government for journalist Irina Slavina's self-immolation. Before taking her own life, Slavina blamed pressure from Russian law enforcement for her decision to take her own life.

CNN's Claudia Otto and Fred Pleitgen contributed to this report.