The poor showing of Russia’s ruling party in Sunday's parliamentary elections will likely create hurdles for Prime Minister Vladimir Putin, who will face voters in March in a presidential election. But this week, a new political player, the Internet, is amplifying charges of electoral fraud and giving a voice to the opposition.

Putin looked glum when President Dmitry Medvedev tried to put a positive spin on elections that cost Russia’s ruling party one quarter of its seats in parliament.

With barely half of Russians voting for the United Russia party, it was the biggest electoral setback for the ruling party since Putin emerged as Russia’s most visible politician 11 years ago. And for the last decade, Putin has been more popular than his United Russia party.

Independent pollster Lev Gudkov says Putin still controls parliament, but his image suffered in these elections.

The ruling party won only one third of the votes cast in St. Petersburg - Putin's and Medvedev's hometown. United Russia won more than 70 percent of the vote in Muslim areas, but only 35 percent of the vote in the nation’s ethnic-Russian heartland.

On Monday, Moscow saw its biggest demonstration in years. Echo Moscow radio warned listeners of streets closed by riot police.

About 6,000 people marched near the Kremlin, with many chanting “Russia without Putin!”

Before joining the march, opposition politician Vladimir Ryzhkov accused government workers of padding election results in Moscow and other major cities.

“The most catastrophic situation for them are Moscow, St. Petersburg, Yekaterinburg - big cities, so-called 'millioniki' - cities with millions of inhabitants. It's absolutely catastrophic for Putin's party," said Ryzhkov. "So the real result is about 30-35 percent [of the vote for United Russia], no more. It means that 10-15 percent [of the ballots] have been falsified.”

European observers say the voting was marred by ballot box stuffing and that vote counting was marred by “frequent procedural violations.”

“Our main concern is the lack of separation between the governing party and the state," said Heidi Tagliavini, a Swiss diplomat who heads an observer team from the Organization for Security and Cooperation in Europe.

U.S. Secretary of State Hillary Clinton, on a visit to Germany on Monday, called for investigations of vote fraud allegations in Russia.

"Russian people, like people everywhere, deserve the right to have their voices heard and their votes counted," she said.

In Moscow, independent media websites recovered Monday from massive hacker attacks that disabled them on election day.

Opposition lawyer Mark Feygin says Russia’s Internet explosion is rapidly changing Russia’s political landscape. He attributes Mr. Putin’s decreasing popularity in Russia’s major cities to increased access to uncensored news on the Internet.

Opposition politician Vladimir Ryzhkov agrees, saying that time is on the side of Russia’s growing number of Internet users.

“Yesterday, it was historic day because this Internet party won and TV party lost,” he said.

Russia recently overtook Germany as the country with the most Internet users in Europe - 51 million people. And analysts say Sunday's parliamentary elections might have been the first time that Vladimir Putin felt their political power.