The Russian opposition politician Alexei Navalny has been detained at Moscow’s Sheremetyevo airport shortly after returning from treatment abroad for a suspected poisoning attempt on his life by Russia’s FSB spy agency.

Navalny, whose investigations into corruption in Vladimir Putin’s inner circle have sparked protests and angered the country’s most powerful men, had vowed to return home despite signs the Kremlin was preparing to arrest him.

Police detained Navalny shortly after his flight from Berlin landed on Sunday evening. It was due to touch down at Moscow’s Vnukovo airport, where hundreds of supporters had gathered. The authorities closed the airport at the last minute, with Navalny’s plane diverted to Sheremetyevo and away from waiting media.

Navalny’s spokesperson Kira Yarmysh said the Kremlin was terrified of Navalny and of images showing large crowds wanting to greet him. “Until recently, it was impossible to believe they [the authorities] were so scared. But here’s the confirmation,” she tweeted.

After landing back in Russia Navalny and his wife left the plane before trundling in an airport bus with other passengers towards the terminal building. He said he was “very happy to be back”, adding: “This is the best day in the last five months”. The criminal cases against him were all fabricated, he said, adding that justice was on his side.

Police officers met Navalny at passport control and detained him. Navalny kissed his wife goodbye and disappeared with the officers.

The official cause was for Navalny’s arrest was failure to appear at a parole hearing. He could face years behind bars if a suspended sentence he received in 2014 is amended to a prison term.

Hundreds of his supporters defied a ban on protests at the airport to meet the returning dissident. Soon before his plane landed ‘Omon’ riot police entered the terminal and arrested dozens. There were cries of “fascists” as supporters were dragged off.

Earlier Navalny was in good spirits on the plane shortly before his arrest, telling journalists who flew with him from Berlin: “I am not afraid”. He said he was “extremely happy” to be returning to Russia after almost five months spent recuperating in Germany.

He joked that he was more concerned by the freezing winter conditions awaiting him in his home city than he was of the authorities. “What bad things could happen to me inside Russia,” he quipped, saying: “I have every right to come back”.

Russian law enforcement had threatened to jail Navalny, in an apparent effort to keep him in exile in Berlin, where he had been recuperating from the poisoning attempt since August. Doctors at Berlin’s Charité clinic identified the poison used against him as a member of the novichok family, similar to the one used in the Salisbury attacks.

While in Berlin, Navalny had participated in an investigation by the website Bellingcat into the attempt on his life, which exposed an FSB hit squad that had shadowed him around the country for years. Navalny personally elicited a confession from a member of the operation in a revelation seen as deeply embarrassing for the agency and for Putin, a former KGB officer and one-time head of the FSB. Putin, who never refers to Navalny by name, had dismissed the Bellingcat report as a “falsification”.

Since then, Russian investigators have increased the pressure on Navalny, who has built a political and investigative operation that has become one of the most vocal and effective critics of Putin and his entourage.

Speaking to the independent TV Rain channel, the opposition activist Vladimir Kara-Murza said a “smart” regime would have ignored Navalny’s return. He described the Putin regime as “not clever” and said it had made strenuous efforts to ensure Navalny stayed in exile.

Kara-Murza likened Putin’s behaviour to that of Yuri Andropov, the Soviet politburo leader and hardline KGB chief. Andropov deported high-profile critics to the west, including the writer Alexander Solzhenitsyn and human rights campaigner Vladimir Bukovsky.

Navalny had every right to return home despite the likelihood of his arrest, Kara-Murza said. He added: “You can only be a Russian politician from within Russia. Outside you lose relevance.”

Moscow’s prison service said earlier this week it had orders to arrest Navalny for missing parole hearings during his convalescence, potentially converting a suspended sentence of three and a half years that expired in December into hard prison time.

And Russia’s Investigative Committee has opened a criminal inquiry into alleged embezzlement from his anti-corruption fund that could carry a decade-long sentence if brought to trial.

Navalny had explained his decision to come home by saying that he had “never considered the decision of whether to return or not”.

“I survived,” he said in a video with more than 1.9m views on Instagram. “And now Putin, who gave the order for my murder, is screaming in his bunker and ordering his servants to do everything to keep me from returning. His servants are acting like they usually do: inventing new criminal cases against me.”

But, he said, he would return nonetheless. “Russia is my country, Moscow is my city, I miss them.”

Russian law enforcement has repeatedly launched criminal investigations against Navalny over the past decade that have kept him in courtrooms or trapped at home on house arrest. His brother Oleg also served three and a half years in prison for the same embezzlement case in which Navalny was given a suspended sentence. He has said the prosecution was political. But authorities have so far avoided giving Navalny a long prison sentence, likely in order to avoid sparking a backlash.