Last updated 7.20pm
Russian police detained Kremlin critic Alexei Navalny at a Moscow airport on Sunday, shortly after he landed on a flight from Berlin.
Navalny's spokeswoman Kira Yarmysh confirmed he had been detained, saying on Twitter: "Alexei was taken away by police officers at the border. With no explanation given."
Navalny arrived on Sunday evening after his flight was diverted at the last minute from Vnukovo Airport where his supporters and media had gathered.
Earlier, Russian police detained top Navalny allies at Vnukovo Airport.
This was Navalny's first return to Russia since a near-fatal poisoning in August.
Officials had warned that they would arrest him for breaking the terms of a suspended prison sentence.
Supporters had gathered at Vnukovo airport around 7:30 pm (1630 GMT), despite the airport banning mass events because of coronavirus restrictions.
With his plane still in the air, police detained top aides including prominent Moscow activist Lyubov Sobol.
Footage shot by local journalists showed police leading her and three others away, while there were reports of at least 10 people detained.
The flight carrying Navalny from Germany, where the 44-year-old spent months recovering from the August poisoning, took off from Berlin's Brandenburg Airport just after 3:15 pm (1415 GMT), according to AFP journalists on the plane.
Wearing a blue face mask, green jacket and scarf, Navalny boarded with his wife Yulia.
Speaking to reporters on the plane, he said he did not fear being arrested on arrival in Moscow.
"They will arrest me? They will arrest me? That's impossible, I'm an innocent person," Navalny said.
"I feel I am a citizen of Russia who has the full right to return to his home."
There was a heavy security presence at Vnukovo, AFP journalists at the airport said, including dozens of police in riot gear with black helmets and batons.
Some Navalny supporters had also gathered, including Tanya Shchukina, an artist who had travelled from Saint Petersburg.
"It is important for me, as a Russian citizen, to support this man, his courage," she told AFP. "After this assassination attempt... I had to come to support him, to show him that he is not alone, that everything will be okay."
- Facing criminal probe -
Navalny fell violently ill on a flight over Siberia in August and was flown out to Berlin in an induced coma.
Western experts concluded he was poisoned with Soviet-designed nerve toxin Novichok and Navalny alleges the attack was carried out on the orders of President Vladimir Putin.
The Kremlin denies any involvement and Russian investigators said there were no grounds to launch a probe into the attack.
Berlin said Saturday it had responded to requests for legal assistance from Moscow and handed over transcripts of an interview conducted by German police with Navalny.
Russian foreign ministry spokeswoman Maria Zakharova on Sunday confirmed that Russia received the documents sent by Germany but they "essentially didn't contain anything" on the questions that Moscow had.
Russia's prison service FSIN says Navalny may face jail time on arrival in Moscow for violating the terms of a 2014 suspended sentence he was handed on fraud charges.
The FSIN said it would be "obliged" to detain Navalny once he returned to Russia.
The anti-graft campaigner may also face criminal charges under a probe launched late last year by Russian investigators who say he misappropriated over $4 million worth of donations.
Navalny and his allies said the authorities were trying to intimidate him into not returning to Russia and encouraged supporters to gather at the airport.
In response to a Facebook event, more than 2,000 people said they were planning to go, despite temperatures in Moscow hovering around -20 degrees Celsius (-4 degrees Fahrenheit).
- Anti-corruption investigations -
Navalny has been the symbol of Russia's protest movement for a decade, after rising to prominence as an anti-corruption blogger and leading anti-government street rallies.
Navalny publishes YouTube investigations into the wealth of Russia's political elites, some of which garner millions of views, making the activist's team a target of lawsuits, police raids and jail stints.
Navalny is ignored or given negative coverage by state-controlled TV, the primary source of news for many Russians, which makes it unclear how much support he enjoys among ordinary citizens.
According to a poll published by the independent Levada Centre last year, only 20 percent of respondents said they approved of Navalny's actions, while 50 percent disapproved.
Navalny has never held elected office. He came second in a 2013 vote for mayor of Moscow but was barred from standing against Putin in the 2018 presidential elections.
His allies are also frequently prevented from running for election.
In 2019, several Navalny allies were barred from running for the Moscow city council, sparking mass rallies in the capital that lasted several weeks.
His team has been gearing up to challenge the ruling United Russia party in elections to the lower house State Duma due in September.