Thousands of people took to Moscow's streets for the fourth weekend in a row to demand that city authorities allow opposition-minded candidates to be allowed on the ballot for the Sept. 8 City Duma elections.

Opposition candidate Lyubov Sobol, virtually the only leading opposition figure who hadn't yet been jailed ahead of Saturday's protest, was detained shortly before the protest was set to begin.

Throughout the rest of the day, 1,001 people were detained, according to the OVD-Info police-monitoring site, sometimes violently.

Saturday's unauthorized protest was smaller than one a week earlier, where more than 1,300 had been detained, but underlined the determination of some Kremlin critics — especially younger people — to keep pressing to open up Russia's tightly-choreographed political system.

Here's a look some of at the most famous images from the most recent protest that have been shared across social media: