Two Russian activists involved in a campaign against what they say are President Vladimir Putin's illegal plans to remain in power were detained by authorities on Thursday and four others had their homes searched, an anti-Kremlin group said.
Moscow's Investigative Committee, which looks into serious crimes, and the city's police force did not immediately respond to comment requests.
Activists had planned a protest in central Moscow on July 15 advertised on social media as "No to an eternal Putin".
A landslide vote this month handed Putin the right to run for two more presidential terms, an outcome the Kremlin described as a triumph. [nL8N2E82EI]
Opposition activists say the vote was illegitimate, marred with violations, and that it's time for Putin, who has ruled Russia for over two decades as president or prime minister, to step down.
Mass gatherings are currently banned in the capital due to Covid-19 restrictions and protests of more than one person require authorities' advance consent in normal times.
Open Russia, a movement founded by Kremlin critic Mikhail Khodorkovsky, said its offices in central Moscow were being searched and that two of its employees, including executive director Andrei Pivovarov, had been detained.
Pivovarov earlier on Thursday posted a link on Twitter encouraging people to attend next week's protest.
Yulia Galyamina, a Moscow city councillor, said police arrived at her apartment early on Thursday and threatened to tear down the door if they weren't let in.
"It's because of the campaign against the (constitutional) reforms," she told Reuters. "It's because of the planned protest."
The homes of Tatiana Usmanova and Olga Gorelik, from Open Russia, were also searched on Tuesday, Open Russia said.
Sergei Prostakov, editor-in-chief of MBKh Media, a news outlet founded by Khodorkovsky, was also targeted by the searches, his organisation said.
Alexei Navalny, a prominent opposition figure, said the searches were designed to scare Kremlin critics.
"This is an attempt to demoralise those who are against Putin and publicly punish those who opposed Putin's amendments," Navalny wrote on Twitter.