The Presnensky district court on August 2 ruled that Ivan Podkopayev, Samariddin Radzhabov, Aleksei Menyailo, and Kirill Zhukov must be placed in pretrial detention center until September 27.

The four were charged with "taking part in mass disturbances" at the July 27 rally, while Zhukov and Radzhabov were also charged with assaulting police.

While dozens of protesters detained in Moscow on July 27 have since been fined or given jail sentences of up to 30 days for organizing and participating in the unsanctioned rally, the charges of mass disturbances are much more serious and can carry a prison sentence of up to 15 years.

Zhukov's lawyer, Svetlana Baiturina, said her client had begun a hunger strike to protest his arrest.

Also on August 2, an unregistered candidate to the Moscow city council, Yegor Zhukov, was charged with taking part in mass disturbances.

Another activist who took part in the rally, Yevgeny Kovalenko, was sent to pretrial detention for two months, on July 29. He was charged with taking part in mass disturbances and assaulting a police officer.

Moscow election officials said earlier in July that they barred some opposition candidates from the September 8 Moscow City Duma election because of insufficient signatures on nominating petitions. The decision had sparked several days of demonstrations last month, including one on July 20 in Moscow that drew an estimated crowd of 20,000.

The 45 members of the Moscow City Duma hold powerful posts -- retaining the ability to propose legislation as well as inspect how the city’s $43 billion budget is spent.

Nearly 1,400 demonstrators were held after the July 27 rally, independent political watchdog OVD-Info says, and security officials in Moscow have been condemned by rights groups and many Western governments and organizations for a "disproportionate" use of force in breaking up the demonstration.

The police crackdown was one of the harshest in recent years against an opposition that has grown more defiant while denouncing Russian President Vladimir Putin’s hold on power.

Nonetheless, opposition activists plan another rally on August 3.

With reporting by Mediazona and Dozhd TV