Five people have been detained as part of criminal proceedings into mass civil unrest related to last weekend’s opposition protest in Moscow, with more apprehensions expected, Russian investigators said.

Police detained more than 1,300 people in central Moscow on Saturday, some violently, at a march in support of fair local elections this fall. Observers have compared the civil unrest case to the aftermath of mass anti-Kremlin demonstrations in 2012, when dozens of activists were prosecuted and jailed.

Authorities suspect 10 or more participants of “taking the most active part in organizing and conducting the mass riots,” the Moscow branch of Russia’s Investigative Committee said Thursday. 

Five people have been detained so far, the Investigative Committee said. Those detained include activists Alexei Minyailo, Kirill Zhukov and Ivan Podkopaev.

“We plan a number of detentions of citizens involved in mass riots and violence against law enforcement and Russian National Guard representatives during the unauthorized rally,” investigators said.

Earlier this week, investigators raided the homes of at least two activists in connection with the criminal case.

The charges for organizing mass riots carry a maximum prison sentence of 15 years.

Several opposition candidates to the 45-seat Moscow City Duma have been jailed as organizers press ahead with new rallies this weekend. 

Lyubov Sobol, a rejected candidate who has been on hunger strike for more than two weeks, called on supporters to gather along central Moscow’s Boulevard Ring for a “peaceful march” Saturday.