Russians voted on Sunday in a parliamentary election seen as a test of Vladimir Putin's personal authority before his planned return to the presidency, and an electoral watchdog complained of 'massive cyber attacks' on a website alleging violations.

Putin remains by far the most popular politician in the vast country of more than 140 million people but there are some signs Russians may be wearying of his cultivated strong-man image after 12 years in power.

The 59-year-old ex-spy looked stern and said only that he hoped for good results for his ruling United Russia party as he walked past supporters to vote in Moscow.

I will vote for Putin. Everything he gets involved in, he manages well, said Father Vasily, 61, a white-bearded monk from a nearby monastery. It's too early for a new generation. They will be in charge another 20 years. We are Russians, we are Asians, we need a strong leadership.

A Western-financed electoral watchdog and two liberal media outlets said their sites had been shut down by hackers intent on silencing allegations of violations. Sites belonging to the Ekho Moskvy radio station, online news portal Slon.ru and the watchdog Golos went down at around 8 a.m.

Massive cyber attacks are taking place on the sites of Golos and the map showing violations, Golos said on Twitter.

I believe that nobody but government structures and the FSB (Security service) is capable of conducting such a campaign, Golos executive director Liliya Shibanova told reporters.

Golos said it had been excluded from several polling booths in the Siberian region of Tomsk. Moscow prosecutors launched an investigation last week into Golos' activities after lawmakers objected to its Western financing.

On Saturday, customs officers held Golos's director for 12 hours at a Moscow airport and Washington said on Friday it was concerned by a pattern of harassment against the watchdog.

Ekho Moskvy editor-in-chief Alexei Venediktov wrote on Twitter: It is obvious the election day attack on the (radio) site is part of an attempt to prevent publishing information about violations.

President Dmitry Medvedev, who is stepping aside next year so that Putin can return to the presidency, has dismissed talk of electoral fraud. The general prosecutor's office and the Central Election Commission could be reached for comment.

SOME RUSSIANS WEARY OF PUTIN

Opinion polls before the vote put Putin's party on course to win a majority but less than the 315 seats it now has in the 450-seat lower house of parliament, the State Duma.

If Putin's party gets less than two-thirds of seats, it would be stripped of its so called constitutional majority which allows it to change the constitution and even approve the impeachment of the president.

Some voters said they would vote for Just Russia, which calls itself 'new socialist', or the Communists, who retain support largely among poorer citizens 20 years after the fall of the Soviet Union and the advent of a free-market system.

United Russia has lost touch with reality, said a 30-year-old history teacher in St Petersburg who gave his name only as Alexander. He was planning to switch his vote to the Communists.

Others in Russia's second city said they would vote for liberal, Western-leaning Yabloko but the biggest liberal opposition group was barred from taking part.

One of its co-leaders, former First Deputy Prime Minister Boris Nemtsov, put a big X across the ballot paper and wrote: Give us back our elections, vermin.

About 30 opposition protesters gathered by the Kremlin screaming: Your elections are a farce! through loudspeakers. Twelve were detained by police, Reuters witnesses said.

Witnesses said police also detained at least 20 people after more than 200 gathered in St Petersburg to protest against election fraud, whistling and chanting: Shameful Elections!

Communist Party leader Gennady Zyuganov, voting at a cultural centre decked out with Soviet-style hammer and sickle flags, said there appeared to be election violations in several parts of the country spanning 9,000 km (5,600 miles).

I just spoke to our people in Siberia and the Far East and the situation is very worrying, he said.

PUTIN'S PARTY

Supporters say Putin saved Russia during his 2000-2008 presidency, restoring Kremlin control over sprawling regions and reviving an economy mired in post-Soviet chaos.

His use of military force to crush a rebellion in the southern Muslim region of Chechnya also won him broad support, and security was tight there on election day.

Opposition parties say the election was unfair from the start because of authorities' support for United Russia with cash and television air time.

Putin has no serious personal rivals as Russia's leader. He remains the ultimate arbiter between the clans which control the world's biggest energy producer.

But his party has had to fight against opponents who have branded it a collection of swindlers and thieves and combat a growing sense of unease among voters at Putin's grip on power.

I shall not vote. I shall cross out all the parties on the list and write: 'Down with the party of swindlers and thieves,' said Nikolai Markovtsev, an independent deputy in the Vladivostok city legislature on the Pacific seaboard.

These are not elections: this is sacrilege, he said.

Opponents say Putin has crafted a brittle political system which excludes independent voices and that Russians are growing tired of Putin's swaggering image.

Putin is almost certain to win the March 4 presidential election and could extend his rule until 2024 if he wins the maximum two more terms.

But sports fans booed and whistled at Putin at a Moscow martial arts fight last month -- an exceptional event in a country inclined to show respect and restraint towards leaders. ($1 = 30.8947 Russian roubles)

(Writing by Ralph Boulton, Editing by Timothy Heritage)