OVD-Info said the number of the detentions it logged for Saturday's protest reached 1,373 by early Sunday. The group has monitored arrests since 2011.
Russian police violently dispersed thousands of people who thronged Moscow streets on Saturday to protest election authorities for disqualifying independent candidates from the September 8 election for the Moscow city council.
Several protesters reported broken limbs and head injuries. Police justified their response by saying the rally was not sanctioned by authorities.
Chants of "Russia without Putin" and "Putin resign" echoed through central Moscow as guardsmen clad in riot gear beat back protesters with batons and roughly detained people, Reuters reported.