Russia's Federal Penitentiary Service confirmed Monday opposition leader and Kremlin critic Alexey Navalny was in its custody. He will remain in detention until a court hearing scheduled for later in January, it said.
Navalny was arrested immediately upon his return to Russia. Navalny has been in Germany for the past five months - recovering from nerve-agent poisoning.
Navalny was arrested by police without explanation, a representative said. The politician's lawyer said police didn't allow him to accompany Navalny and he was currently determining where his client had been taken.
Local news recorded the arrest. Uniformed and masked officers removed Navalny from the airport. Russia broadcaster TV Rain showed him and his wife before the arrest.
Navalny and his wife landed at Sheremetyevo International Airport late Sunday local time. The opposition leader has been on Russia's federal wanted list since last month. He is accused of violating terms of probation related to a fraud case - which Navalny had described as "politically motivated."
"Everyone is asking me if I'm scared. I am not afraid. I feel completely fine walking toward border control. I know that I will leave and go home because I'm right and all the criminal cases against me are fabricated," Navalny said as he was arrested.
Hundreds of Navalny's supporters had gathered at an airport in Vnukovo where his flight was scheduled to land. Sources said Navalny's flight was likely diverted at the last minute to Sheremetyevo.
Navalny was poisoned in August while on a commercial flight. Independent investigations found evidence that implicated Russia's security service. An elite Federal Security Service unit allegedly followed Navalny throughout his trip to Siberia and his return to Moscow.
Russian President Vladimir Putin has denied any involvement. Putin previously said if the security service wanted him dead they "would have finished the job."