MOSCOW (NewsNation Now) —  Russian opposition leader Alexei Navalny was detained at a Moscow airport after returning from Germany on Sunday, the prison service said.

The prison service said he was detained for multiple violations of parole and terms of a suspended prison sentence and would be held in custody until a court makes a decision in his case.

Navalny, who is President Vladimir Putin’s most prominent and determined foe, was returning from Germany, where he spent five months recovering from poisoning by a nerve agent, which he blames on the Kremlin.

Navalny supporters and journalists had come to Moscow’s Vnukovo Airport, where the plane was scheduled to land, but it ended up touching down at Sheremetyevo airport, about 40 kilometers (25 miles) away. There was no immediate explanation for the flight diversion.

Russia’s prison service last week issued a warrant for his arrest, saying he had violated the terms of suspended sentence he received on a 2014 conviction for embezzlement. The prison service has asked a Moscow court to turn Navalny’s 3 1/2-year suspended sentence into a real one.

After boarding the Moscow flight in Berlin on Sunday, Navalny said of the prospect of arrest: “It’s impossible; I’m an innocent man.”

Vnukovo Aurport banned journalists from working inside the terminal, saying in a statement last week that the move was due to epidemiological concerns. The airport also blocked off access to the international arrivals area.

Police prisoner-detention vehicles stood outside the terminal on Sunday.

The independent newspaper Novaya Gazeta and opposition social media reported Sunday that several Navalny supporters in St. Petersburg had been removed from Moscow-bound trains or been prevented from boarding flights late Saturday and early Sunday, including the coordinator of his staff for the region of Russia’s second-largest city

Navalny recovered in Germany from his poisoning in August with a nerve agent, which he has blamed on the Kremlin. The Kremlin has repeatedly denied a role in the opposition leader’s poisoning.

He announced Wednesday that he would return home despite Russian authorities’ threats to put him behind bars again. Russia’s prison service said that he faces immediate arrest once he returns.

Navalny said as he boarded the plane that he was “very happy.”

Navalny has charged that Russian President Vladimir Putin was now trying to deter him from coming home with new legal motions.

At the end of December, the Federal Penitentiary Service, or FSIN, warned Navalny that he faced time in prison if he fails to immediately report to its office in line with the terms of a suspended sentence and probation he received for a 2014 conviction on charges of embezzlement and money laundering that he rejected as politically motivated. The European Court for Human Rights had ruled that his conviction was unlawful.

The FSIN said Thursday it issued an arrest warrant for Navalny after he failed to report to its office. The prison service, which has asked a Moscow court to turn Navalny’s 3 1/2-year suspended sentence into a real one, said it’s “obliged to take all the necessary action to detain Navalny pending the court’s ruling.”

Navalny fell into a coma while aboard a domestic flight from Siberia to Moscow on Aug. 20. He was transferred from a hospital in Siberia to a Berlin hospital two days later.

Labs in Germany, France and Sweden, and tests by the Organization 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 Navalny in Siberia before he was airlifted to Germany found no traces of poison and have challenged German officials to provide proof of his poisoning. They refused to open a full-fledged criminal inquiry, citing a lack of evidence that Navalny was poisoned.

Last month, Navalny released the recording of a phone call he said he made to a man he described as an alleged member of a group of officers of the Federal Security Service, or FSB, who purportedly poisoned him in August and then tried to cover it up. The FSB dismissed the recording as fake