Thousands of demonstrators converged on central Moscow Saturday to protest Russian President-elect Vladimir Putin's third term in office. But the protest failed to reach the scale of recent demonstrations, in a sign the opposition might be losing momentum.

Leftist opposition leader Sergei Udaltsov was one of several people arrested in Moscow Saturday after he tried to lead an unsanctioned march at the end of the rally. About 40 people were arrested at an unsanctioned rally in St. Petersburg.

The demonstrators are challenging the authority of Mr. Putin, who won 64 percent of the vote in the March 4 election.

“Today's main message is, those observers who were brave enough to participate in the observation of the voting day, today they are sharing their views, how just lawlessness took place during this voting day, and in fact, that is an additional part of the overall protest movement.”

Protests against Mr. Putin began after allegations of fraud in the December parliamentary election, which saw his ruling United Russia party win 238 of 450 seats.

Mr. Putin served as president from 2000-2008, but term limits prevented him from running for a third consecutive term. He then became prime minister – a position he currently holds.

Tens of thousands of people took to the streets in Moscow and elsewhere after the December vote demanding a rerun of the elections in the largest-ever demonstrations in post-Soviet Russia.