Vladimir Putin's ruling party suffered a surprise drop in support Sunday in legislative elections seen as a test of the Russian strongman's popularity ahead of his planned return to the Kremlin.

United Russia was on course to win but with less than half the votes, exit polls and initial results based on around a fifth of the count showed, in an unexpected blow to its supreme dominance of Russian politics.

The decline in its support came after an election marred by allegations the authorities had committed major violations to ensure the party hung on to an overwhelming parliamentary majority.

United Russia won 45.9 percent of the vote, based on over 17 percent of the precincts reporting, the central election commission said. The Communist Party was second with 20.7 percent, the commission added.

The results mark a major reverse from the last parliamentary elections in 2007 when United Russia secured a landslide majority of 64.3 percent and won 315 seats in the 450 seat State Duma.

Standing alongside President Dmitry Medvedev in a live televised address, Putin put a brave face on the results and made no specific mention of the fall in support.

"Based on these results, we will be able to ensure the stable development of our country," Putin said.

Medvedev, for his part, rejected the claims of foul play by the authorities, saying the elections results showed Russian "democracy in action" and reflected voters' true moods.

The ultra-nationalist Liberal Democratic Party was third with 14.3 percent while the populist A Just Russia group had 13.3 percent of the vote, the early results quoted by the election commission said.

It is not yet clear how the results will translate into seats and if United Russia is at risk of losing its overall majority in the Duma.

"The result is not a catastrophe for United Russia," said Yevgeny Volk, analyst with the Yeltsin Foundation. "But it shows that there is a disappointment with the ruling party."

The four parties, all members of the outgoing State Duma lower house of parliament, were the only ones to break through the seven-percent vote barrier necessary for proportionate party representation in the chamber.

Veteran liberal politician Grigory Yavlinsky's Yabloko party trailed in fifth place with 2.6 percent of the vote, the early results showed.

Exit polls all showed United Russia also winning less than 50 percent of the vote. The All-Russian Public Opinion Research Centre (VTsIOM) said United Russia was to win 48.5 percent of the vote, ahead of the Communist Party with 19.8 percent.

The four years since the last parliamentary vote have been marked by an outburst of criticism of the authorities on the Internet as web penetration of Russia started to finally catch up with the rest of Europe.

Putin was recently subjected to unprecedented booing when he made an appearance at a martial arts fight and opinion polls have shown chinks in his once impregnable popularity.

The Russian strongman is standing in March 2012 presidential elections to return to the Kremlin after his four-year stint as prime minister. His protege Medvedev is set to cede the Kremlin and become prime minister.