Russian opposition figure and Putin critic Alexei Navalny has returned to Moscow where he was detained at border control, moments after arrival from Germany where he underwent treatment and rehabilitation following a poisoning attack with what international experts believe was a novichok-type agent.

According to Flightradar24, Navalny's flight operated by Russia's Pobeda carrier has landed at Moscow's Sheremetyevo airport at 19:20 local time after being redirected from its initial destination, Vnukovo, as reported by Dozhd.

The airline's press service said in a statement that the rerouting was due to "technical" issues at Vnukovo where a crowd gathered to meet Navalny amid massive police presence.

According to Russian media reports, dozens were detained at Vnukovo over an "unauthorized rally".

Meanwhile, the Federal Penitentiary Service has confirmed Navalny's arrest, as per TASS.

The statement recalls that Navalny had earlier been handed down a conditional sentence and put on wanted list on December 29, 2020, for "repeated violations of probation terms."

Further measures to be applied to Alexei Navalny will be determined by court.

"Until the court issues its ruling, he will remain in custody," said the statement.

Read alsoRussia puts Navalny on wanted listNavalny poisoning: Background

Kremlin critic Alexei Navalny felt sick on board the plane he was flying from the city of Tomsk to Moscow on August 20. His rapidly deteriorating condition forced the captain to perform an emergency landing in Omsk.

Navalny was evacuated from Omsk to Berlin's Charite hospital on an ambulance aircraft for further medical treatment on August 22.

On September 4, it was announced that experts with the Bundeswehr laboratory had found traces of poison from the Novichok group in Navalny's body. In this regard, Berlin called on Moscow to explain the circumstances of the poisoning of the Russian opposition figure.

On September 10, it was reported Navalny had made further progress in his recovery and was able to speak again.

On September 14, French and Swedish laboratories independently confirmed Navalny had been poisoned with a chemical nerve agent of the Novichok group.

On September 23, he was discharged from Charite. He is now convalescing in a secret location.

On September 25, Navalny's press secretary, Kira Yarmysh, said that the opposition leader would remain in Germany until the end of his rehabilitation course.

On October 1, speaking in an interview for Germany's Der Spiegel, Navalny said that Russian President Vladimir Putin personally stood behind the attempt to poison him with Novichok. Navalny said he planned to return to Russia.

In a prank call late December, Navalny duped a Russian secret agent into disclosing details of the botched plot to kill him and had been told that poison had been placed in his underpants.