MOSCOW (Reuters) - Russian opposition leader Alexei Navalny was detained by police on Saturday after arriving at a rally in central Moscow to protest against President Vladimir Putin, an ally of the politician said.

Navalny had called on Kremlin critics to take to the streets on Saturday ahead of Putin’s inauguration for a fourth presidential term to register their opposition to what Navalny says is Putin’s autocratic Tsar-like rule.

“Navalny appeared on Pushkinskaya (Square) and was quickly detained,” Leonid Volkov, an opposition politician, said in an online broadcast. “It (the detention) was absolutely illegal.”