Updated at 11:40 a.m. ET: MOSCOW -- Russia's presidential election was clearly skewed in favor of Prime Minister Vladimir Putin, international vote monitors said in a report on Monday.

"There was no real competition and abuse of government resources ensured that the ultimate winner of the election was never in doubt," Tonino Picula, one of the vote monitors from the Organization for Security and Co-Operation in Europe, said in a statement.

Monitors cited "serious problems" with the vote and called for alleged electoral violations in Sunday's election to be thoroughly investigated.

Golos, Russia's leading independent elections watchdog, earlier said it had registered at least 3,100 reports of violations nationwide.

Golos cited received numerous reports of "carousel voting," in which busloads of voters are driven around to cast ballots multiple times.

The Central Elections Commission said Putin got more than 63 percent of the nationwide vote. However, Golos said that incomplete reports from its observers of individual polling station counts indicate Putin hovered perilously close to the 50-percent mark needed for a first-round victory.

Accounts of extensive vote-rigging looked set to strengthen the resolve of opposition forces whose unprecedented protests in recent months have posed the first serious challenge to Putin's heavy-handed rule.

Anti-Putin activists pay high price

Putin said the presidential election had prevented Russia from falling into the hands of enemies. Complaining of widespread fraud, his opponents said they would rally near the Kremlin on Monday night.

His eyes brimming with tears, the former KGB spy defiantly proclaimed to a sea of supporters that they had triumphed over opponents intent on "destroying Russia's statehood and usurping power."

Putin's win was never in doubt as many across the vast country still see him as a guarantor of stability and the defender of a strong Russia against a hostile world, an image he has carefully cultivated during 12 years in power.

'Honest struggle'
Putin claimed victory Sunday night when fewer than a quarter of the votes had been counted. He spoke to a rally just outside the Kremlin walls of tens of thousands of supporters, many of them government workers or employees of state-owned companies who had been ordered to attend.

"I promised that we would win and we have won!" Putin shouted to the flag-waving crowd. "We have won in an open and honest struggle."

He ended his speech with the triumphant declaration: "Glory to Russia!"

Putin was president from 2000 until 2008, before moving into the prime minister's office due to term limits.

Putin, 59, is on collision course with the mainly middle-class protesters who have staged rallies in the capital and other big cities since since December.

Corruption
The wave of protests began after a parliamentary election in which observers produced evidence of widespread vote fraud. Protest rallies in Moscow drew tens of thousands in the largest outburst of public anger in post-Soviet Russia, demonstrating growing exasperation with the pervasive corruption and tight controls over political life under Putin.

The protest organizers, who see Putin as an autocratic leader whose return to power will stymie hope of economic and political reforms, said their demonstrations would now grow.

"He is forcing things to breaking point. He is declaring war on us. As a result the base of aversion to him is growing," said journalist Sergei Parkhomenko, one of the leaders of the opposition protest movement.

"These elections are not free. ... That's why we'll have protests (Monday)," said Mikhail Kasyanov, who was Putin's first prime minister before going into opposition. "We will not recognize the president as legitimate."

Putin's campaign chief, Stanislav Govorukhin, rejected the claims of violations, calling them "ridiculous."

Putin in power until 2024? 10 key questions about the Russian election

Partial results, with nearly 100 percent of the votes counted, put Putin on almost 64 percent of the votes.

His nearest rival, Communist Party leader Gennady Zyuganov, was on about 17 percent of votes, and nationalist Vladimir Zhirinovsky, former parliamentary speaker Sergei Mironov and billionaire Mikhail Prokhorov were below 10 percent.

Ivan Sekretarev / AP

Russian Prime Minister Vladimir Putin, who claimed victory in Sunday's presidential election, gets emotional during a rally in Moscow on Sunday.

Prokhorov, the owner of the NBA's New Jersey Nets, won plaudits for his campaign. He said on Channel One television after the vote that his observers had been kept away from some polling stations and were beaten on two occasions.

Zyuganov said his party would not recognize the result and called the election "illegitimate, dishonest and not transparent".

Despite the opposition, mainly among well-educated and relatively well-off young professionals, Putin's support remains high in the provinces and his victory had not been in doubt.

Putin got more than 90 percent of the vote in several Caucasus provinces, including 99.8 percent in Chechnya.

Television presenter and journalist Tina Kandelaki, a Kremlin supporter who nonetheless found her Unreal Politics discssion programme censored last year, was among a panel appointed by Putin to monitor election fraud.

She told msnbc.com on Monday: "Every complaint will be considered separately and we will do our best to punish law-breakers. All those cases are being checked now. If these complaints are confirmed, we’ll submit cases to the court."

However, she claimed a complaint that 300 buses carrying voters from the province of Dagestan to the central Moscow was examined and "after checking it wasn't confirmed".

Asked about the longer-term implications of Putin's victory, she said: "I'm pretty sure that there would be some political concessions...and the situation with the opposition would change as well." She also believes the process of registration for political parties would be "simplified".

Economic boom
The initial challenge for the man credited by many Russians with rebuilding the country's image and overseeing an economic boom in his first presidency, had been to win more than half the votes on Sunday and avoid a second-round runoff.

His clear victory will enable him to portray his return to the presidency as a strong sign of public support against the protesters, whom he has portrayed as a destabilizing minority and pawns of foreign governments.

But the mood has shifted in the country of 143 million and the urban protest movement portrays him as an obstacle to change and the guardian of a corrupt system of power.

Putin, who will be inaugurated in May, is likely to revert to the fighting talk against the West that was the hallmark of his first presidency and his election campaign.

The West can expect Putin to continue the tough policies he has pursued even as prime minister, including opposing U.S. plans to build a missile shield in Europe and resisting international military intervention in Syria.

"Putin is a brave and persistent man who can resist the U.S. and EU pressure," said Anastasia Lushnikova, a 20-year-old student who voted for Putin in the southern city of Rostov-on-Don.

The Associated Press and Reuters contributed to this report.

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