Thousands of Russians have taken to the streets of Moscow for two opposing rallies — for and against Vladimir Putin's landslide victory in the presidential election Sunday.

There were no arrests reported on central Moscow's Pushkin Square, where opposition groups had received permission to hold a rally. But police arrested Eduard Limonov, the leader of the banned National Bolshevik Party, and several dozen of his supporters, who attempted to hold a separate unsanctioned protest. About 100 protesters were also arrested in St. Petersburg.

International observers say the election was clearly skewed to favor Mr. Putin. Preliminary results give Mr. Putin 64 percent of the vote and his closest rival, Communist Party chief Gennady Zyuganov, 17 percent. Three other candidates won less than 10 percent.

A statement from the Organization for Security and Cooperation in Europe says there was no real competition. It says abuse of government resources ensured that the winner was never in doubt.

The OSCE says Mr. Putin was given a clear advantage in access to the media. It says voters had a limited choice of candidates because of overly restrictive registration requirements. The OSCE also reports voting irregularities at one-third of the polling stations.

On Monday, European leaders acknowledged Mr. Putin's victory with reservations. European Union foreign affairs chief Catherine Ashton urged the Russian leaders to address the “shortcomings” identified by international observers.

Mr. Putin says he won what he calls an “open and honest struggle.” He tearfully greeted tens of thousands of supporters outside the Kremlin Sunday, thanking them for stopping the country from, in his words, “falling into the hands of enemies trying to usurp power.”

The late Russian President Boris Yeltsin had picked Mr. Putin as his successor. Mr. Putin became acting president at the start of 2000 after Mr. Yeltsin stepped down. Mr. Putin won a presidential election later that year and again in 2004. The constitution barred him from a third consecutive term. Mr. Putin has served as Russian prime minister for the last four years under outgoing president Dmitry Medvedev.

Mr. Putin's critics say he planned to return to the presidency all along and that he never really gave up his powers. A constitutional amendment has extended the president's time in office to two consecutive six-year terms, meaning Mr. Putin could stay in power until 2024 — an outlook many Russians find unsettling.

Communist Party candidate Zyuganov denounced Sunday's election as “illegitimate, unfair and not transparent.” Others complained of doctored voting lists and said pro-Kremlin business leaders installed voting booths in factories and pressured workers to vote for Mr. Putin.

Mikhail Gorbachev, the last Soviet leader, told the Interfax news agency that he doubts the results reflect the true will of Russians. He said the challenge now is to change the country's election system to make voting fair, and restore direct election for governors.