Riot police dispersed protesters who tried to prolong an opposition rally in downtown Moscow on late Monday, detaining hundreds, including prominent whistleblower Alexei Navalny and leftist leader Sergei Udaltsov.

Between 14,000 and 20,000, according to various estimates, came to downtown Pushkinskaya Square on late Monday for a sanctioned rally to protest Prime Minister Vladimir Putin’s overnight victory at the presidential polls, which protesters say were rigged.

The event was peaceful, but some 3,000 refused to leave the venue after the rally’s end, State Duma deputy Ilya Ponomaryov, a speaker at the rally, told Dozhd online television.

Ponomaryov said the follow-up event was formally a meeting with him, which means it required no police sanction. But riot police insisted the event was unsanctioned and told the protesters to disperse.

Officers eventually formed a human chain and moved to push protesters from the square. They also used smoke bombs, Gazeta.ru said.

An amateur video from the site run by Dozhd showed officers march across the square and demand that the public leave the venue. It did not show them detaining anyone.

Several hundreds of protesters expelled from Pushkin Square staged an improvised rally, marching away from the Kremlin down the Tverskaya Street. Police tried to disperse them by the nearby Triumfalnaya Square, also detaining some. Meanwhile, between 30 and 40 protesters trickled back to Pushkin Square, shouting opposition slogans.

In total, 250 were detained after protest events in Moscow on Monday, city police said.