A US envoy on Monday hailed the thousands of Russians who took to the streets to criticize President Vladimir Putin, saying they showed bravery.
Russia's opposition called the rally in central Moscow on Saturday, the fifth anniversary of the assassination of leading liberal Boris Nemtsov, to warn Putin not to try to stay in power indefinitely.
Jim Gilmore, the US ambassador to the Organization for Security and Co-Operation in Europe, the East-West body set up during the Cold War to resolve crises and promote democratic standards, said he wanted to "congratulate the thousands of brave Russians who marched on Saturday."
The protesters sought "to make a point about their quest not only for justice but also for a government that's more accountable to the people," he told reporters in Washington.
Unlike demonstrations last summer urging fair elections that were roughly dispersed, Moscow authorities gave permission to the rally.
"Vladimir Putin appears to still have to be responsive somewhat to the Russian people," Gilmore said.
Speaking of the protesters, he said: "They do represent a certain strata of Russian society that we think is deserving of encouragement."
Putin, who has dominated Russia for two decades, has proposed an overhaul of the constitution. Amendments include a mention of God and a stipulation that marriage is only between a man and a woman.
Analysts see the plan as beginning preparations for succession when Putin's fourth presidential term ends in 2024, while the opposition says the Kremlin strongman wants to remain leader for life.
Putin in the past has accused the United States of whipping up protests, claims dismissed by the opposition and the State Department.
Opposition supporters march in memory of murdered Kremlin critic Boris Nemtsov in downtown Moscow on February 29, 2020