When the riot police demanded that the crowd disperse after a couple of hours, many refused to leave. The police then swept up the blogger Aleksei Navalny, the most charismatic figure to emerge in this wave of activism, and dozens of other activists and pushed them into police vans. The police said 250 people had been detained, though many were released early Tuesday morning.

An additional 300 people were detained after a similar event in St. Petersburg.

The arrests drew criticism from the American ambassador, Michael A. McFaul, who said via Twitter that it was “troubling to watch arrests of peaceful demonstrators at Pushkin Square.” Mikhail D. Prokhorov, the billionaire oligarch who placed third in Sunday’s election, wrote over Facebook that he was “indignant over the use of force against people who came to express their civic position.”

In Washington, the reaction to the election was strikingly muted, even restrained. The White House did not comment, and the State Department put out a written statement congratulating the Russian people and saying the United States “looks forward to working with the president-elect after the results are certified and he is sworn in.”

While it noted concerns about “the conditions under which the campaign was conducted, the partisan use of government resources and procedural irregularities on election day,” the statement also praised pledges by the authorities to increase transparency in elections and restore elections for regional governors.