GENEVA: The UN human rights office called on Monday for the immediate release of Kremlin critic Alexei Navalny who is being held in a police station a day after arriving back in Russia for the first time since he was poisoned last year.

"We are deeply troubled by the arrest of Aleksei Navalny, and call for his immediate release and for his due process rights to be respected in line with the rule of law," the Geneva-based rights office said in a statement on Twitter.