West rallies behind seized Kremlin critic

Officials from the US, Europe and the UK have spoken of their "deep concern" over the arrest in Moscow of Russia's opposition leader Alexei Navalny.

Navalny was detained as he landed back on Russian soil on Sunday after spending five months in Germany recovering from nerve agent poisoning that he blames on the Kremlin.

Prior to his arrival at Moscow's Sheremetyevo airport, Russia's prison service said the 44-year-old had violated parole terms from a suspended sentence on a 2014 embezzlement conviction.

Officials said he would be held in custody until a court rules on his case.

Navalny has been a thorn in the Kremlin's side for a decade, unusually durable in an opposition movement often demoralised by repression.

He has been jailed repeatedly in connection with protests and twice was convicted of financial misdeeds in cases that he said were politically motivated.

Navalny's latest detention has been condemned by governments around the world.

US Secretary of State Mike Pompeo said he is "deeply troubled" by Navalny's arrest, while adding a veiled criticism of Russian President Vladimir Putin.

"Deeply troubled by Russia's decision to arrest Aleksey Navalny," Pompeo wrote on Twitter.

"Confident political leaders do not fear competing voices, nor see the need to commit violence against or wrongfully detain, political opponents."

A statement from the UK's Foreign, Commonwealth & Development Office (FCDO) said: "We are deeply concerned by the detention on 17 January of Alexei Navalny.

"Instead of persecuting the victim of this terrible crime, the Russian authorities should investigate how a chemical weapon came to be used on Russian soil."

European Parliament President David Sassoli called for Navalny's immediate release.

"The arrest of Alexey #Navalny in Moscow is an offence to the international community, to Europe that helped save his life," he wrote.

"We ask the Russian authorities for his immediate release."

Germany's Foreign Minister Heiko Maas said in a statement that Navalny's detention is "utterly incomprehensible. Rule of law & protection of civil rights, to which Russia is bound by constitution & international obligations, must apply to him. He should be immediately released."

Russia's Foreign Minister Sergey Lavrov said the reaction to Navalny's arrest reflected an attempt "to divert attention from the crisis of the Western model of development".

"Navalny's case has received a foreign policy dimension artificially and without any foundation," Mr Lavrov said, arguing that the opposition leader's detention was a prerogative of Russian law enforcement agencies.

"It's a matter of observing the law," he said.

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

Labs in Germany, France and Sweden 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.