Within hours of the Friday sermon, grainy cellphone videos surfaced showing crowds surging away from tear-gas plumes and kicking the canisters back toward police.
The quick response underlines the rising profile of the social media site as it becomes a breaking news source.
Natalia Estemirova, who has long documented abuses by government-backed militias, is the fourth prominent critic of Kremlin policies to be killed in three years.
Despite a new poll showing firm public support, the deaths of eight troops in 24 hours last week is raising fresh questions about the end goals of the war.
Ahead of a sermon by Mousavi supporter Hashemi Rafsanjani, protesters have taken their fight off the streets – including trying to crash the electricity grid by turning on kitchen appliances en masse.
The teenager disappeared June 15, when hundreds of thousands rallied in Tehran. Officials notified his mother of his death only on Saturday, despite her repeated inquiries at courts and prisons.
The attacks underscore the security challenges after the US withdrawal from cities, particularly in the volatile areas in the north.