Tens of thousands took to the streets across Russia, chanting slogans against President Vladimir Putin, to demand the release of opposition leader Navalny.
Police detained more than 3,800 people, according to a monitoring group, and some protesters were beaten.
The United States urged Russia to release Navalny and criticized the crackdown on protests.
“The US condemns the persistent use of harsh tactics against peaceful protesters and journalists by Russian authorities for a second week straight,” US Secretary of State Antony Blinken said on Twitter.
“We renew our call for Russia to release those detained for exercising their human rights, including Aleksey Navalny,” he added.
Russia’s Ministry of Foreign Affairs slammed Blinken’s call: “The United States’ flagrant interference into Russia’s domestic fairs is a fact in evidence, as is propagation of fakes and calls for unauthorized protests by Washington-controlled internet platforms,” state-news agency TASS reported.
“Another evidence of Washington’s behind-the-scenes role is US State Secretary Antony Blinken’s support to law violations. No doubts that actions geared to encourage protests are an element of the strategy of containing Russia,” the ministry added.
Russian authorities mounted a massive effort to stem the tide of demonstrations after tens of thousands rallied across the country last weekend in the largest, most widespread show of discontent that Russia has seen in years.
Yet despite threats of jail terms, warnings to social media groups and tight police cordons, the protests again engulfed cities across Russia's 11 time zones on Sunday.
On Sunday, police detained more than 3,800 people at protests in cities nationwide, according to OVD-Info, a group that monitors political arrests.
In Moscow, authorities introduced unprecedented security measures in the city center, closing subway stations near the Kremlin, cutting bus traffic and ordering restaurants and stores to stay closed.
The 44-year-old Navalny, an anti-corruption investigator who is Putin's best-known critic, was arrested on January 17 upon returning from Germany, where he spent five months recovering from nerve-agent poisoning that he blames on the Kremlin.
Russian authorities have rejected the accusations. He was arrested for allegedly violating his parole conditions by not reporting for meetings with law enforcement when he was recuperating in Germany.
- With The Associated Press