January 18, 2021: Police on Sunday detained Russia's leading opposition figure and chief Kremlin critic Alexey Navalny, moments after he returned to Moscow.

According to a report by CNN, Navalny was taken away "by police officers at the border" without explanation, his spokesperson Kira Yarmysh tweeted. "The lawyer was not allowed to go with him, because just seconds ago 'he passed the border'."

The 2.5-hour flight by Russian carrier Pobeda took off from Berlin Brandenburg Airport and was due to land in Moscow's Vnukovo, which was heavily guarded by police on Sunday, reported CNN. However, it was diverted to Moscow's Sheremetyevo airport just after 8 pm (local time), as per the flight data information.

Navalny arrived in Germany five months ago in a coma after being poisoned by Novichok, a military-grade nerve agent developed by Russia during the Soviet years. Several Western officials along with Navalny himself have openly blamed Russia for the poisoning, while the Kremlin has denied the allegations.

In a social media post on Wednesday, Navalny had told his supporters to meet him when he lands in Moscow.

"They are doing everything to scare me...But what they are doing there is not of much interest to me. Russia is my country, Moscow is my city, I miss it," said Navalny said in an Instagram post and video on Wednesday.

According to CNN, Moscow authorities issued a warning for those planning to meet Navalny at the airport, saying the city viewed this gathering as an unsanctioned demonstration.

Navalny was placed on the country's federal wanted list during his time in Germany at the request of the Federal Penitentiary Service FSIN's, which had accused him in December 2020 of violating probation terms in a fraud case that was dismissed by Navalny as "politically motivated".

Now the FSIN alleges that Navalny has been in violation of the terms of his suspended sentence by failing to show up for scheduled inspections.

CNN reported that if Navalny is not convicted later in January, he will still face an investigation for a newer fraud case, in which he and his Anti-Corruption Foundation have been accused of misusing donations from supporters.

Political observers are speculating on several possible scenarios, from immediate arrest to a laborious charade of legal threats and short-term detentions.

Abbas Gallyamov, a political consultant and former Kremlin speechwriter, said on Facebook that Navalny would "definitely" be arrested.

"Why am I so sure? Because by initiating these legal cases, the Kremlin has created an expectation within the society... Should it back out of this now, everyone would see it as a weakness, and most of all, [Putin] is afraid to do anything deemed weak," wrote Gallyamov.

"The situation with Navalny looks like two trains running towards each other at full speed, bound to collide... There will be many victims," said Tatyana Stanovaya, a visiting fellow, also at the Carnegie Moscow Center.

Navalny's future could also hang on the reaction of the Russian public to his return and possible arrest. So far, the Kremlin's message on the poisoning has largely resonated with Russians, reported CNN.