By Timothy Heritage and Guy Faulconbridge
MOSCOW, March 4 (Reuters) - Vladimir Putin won a resounding victory in Russia's presidential election on Sunday, exit polls showed, securing a new six-year term in the Kremlin and a mandate to deal with opposition protests after a vote that opponents said was marred by fraud.
Two television exit polls, released after voting ended at 1700 GMT, forecast the prime minister would win 59.3 and 58.3 percent of the votes, easily enough to make a runoff against the second-placed candidate unnecessary.
His nearest rival, Communist Party leader Gennady Zyuganov, fell short of 20 percent in both exit polls. Zyuganov said his party would not recognise the official results of the election, calling it "illegitimate, dishonest and untransparent."
Putin's swiftly dismissed fraud allegations, which will be repeated at opposition protests starting on Monday.
"This is the cleanest election in Russia's entire history," said Stanislav Govorukhin, his campaign chief. "The violations our rivals and the opponents of our president will now speak of are laughable."
Official results are not expected from most polling stations until Monday.
But Putin, 59, was expected to portray his return to the presidency after four years as prime minister as strong public backing against the protesters, whom he has portrayed as a minority and pawns of foreign governments.
A huge crowd of mostly young Putin supporters gathered in a square outside the Kremlin after dark, waving Russian flags. Hundreds of buses that brought them to the capital in a well organised show of force stood by.
The former KGB spy is also expected to return to the Kremlin with tough fighting talk against the West, a trademark of his first presidency and election campaign. Economists said a key test of Putin's return would be how far he was ready to go to reform an economy heavily dependent on energy exports.
But Putin's opponents said voting in many parts of the vast country was skewed in his favour and vowed to press on with the biggest protests since he rose to power 12 years ago.
"We do not consider these elections legitimate," said Vladimir Ryzhkov, a leader of the opposition protesters, who plan a new rally against Putin in Moscow for Monday.
SUPPORT IN THE PROVINCES
Despite the growing opposition, mainly among well-educated and relatively well-off young professionals in big cities, Putin's support remains high in the provinces and his victory had not been in doubt.
The main challenge for the man credited by many Russians credit with rebuilding the country's image and overseeing an economic boom, was to win outright in the first round.
This he achieved by a clear margin. The exit polls put Zyuganov on target to win about 18 percent, and nationalist Vladimir Zhirinovsky, ex-parliamentary speaker Sergei Mironov and billionaire Mikhail Prokhorov were all under 10 percent.
Some voters said Putin, who has portrayed himself as a man of action and guardian of stability, was the tough national leader the world's biggest country and energy producer needed.
"I voted for Putin because he was a good president (from 2000-08) and our children were looked after and that's all. That's how I feel," said Maria Fedotova, a 92-year-old grandmother in fur coat and hat, flanked by relatives.
Putin has remained Russia's dominant leader and its most popular politician since stepping aside in 2008 to make way for his ally, Dmitry Medvedev, because he was barred from a third straight term by the constitution.
But some voters are tired of his macho antics, such as horse riding bare-chested, and a system that concentrates power in his hands. They fear he could win another term in six years and rule until 2024 - almost as long as Soviet dictator Josef Stalin.
"They are stealing our votes," said Valentin Gorshun, a patient in Moscow hospital number 19, where more than 90 percent of votes went to United Russia party in December.
"It is probably the same at all hospitals," he said. "I think they are preparing a huge falsification. Emperor Putin has decided everything."
WIDESPREAD ALLEGATIONS OF FRAUD
Vote monitors from the opposition and bloggers posted allegations of election rigging across the country of 143 million. Golos, an independent monitoring group, said it had registered at least 3,100 reports of violations nationwide.
An Interior Ministry spokesman denied there had been any major violations. Election officials also dismissed reports of widespread fraud in a parliamentary election on Dec. 4 which triggered the opposition protests.
Thousands of opposition activists as well as an international observer mission were also monitoring the polls.
The opposition protests were sparked by the disputed Dec. 4 election, but anger was focused at Putin, who bungled the Sept. 24 announcement of his presidential bid by appearing simply to inform Russians that he would rule for another six years.
Putin, who will not formally take office until early May, now faces huge economic and political challenges.
"It's a watershed - Russia faces decline and stagnation unless they really kick-start reforms, and push forward an ambitious reform agenda," said Tim Ash, head of emerging markets research at Royal bank of Scotland in London.