Russia sees anti and pro-Kremlin rallies in Moscow Reuters

The Kremlin mobilised thousands of police, interior troops and pro-government youth groups on Tuesday night to crack down on protests against the rule of Vladimir Putin after elections that saw his party returned to power with a greatly reduced majority.

Riot police, clad in camouflage and black crash helmets, arrested around 250 people who had gathered at Moscow's Triumphal Square in an attempt to build a wave of demonstrations following Sunday's disputed parliamentary election, in which support for Putin's United Russia party fell below 50%.

But the protesters were vastly outnumbered by pro-Kremlin youth activists, who converged on the square waving huge Russian flags and shouting "Medvedev, victory!" and "Putin, Russia!".

It was the first time the youth group Nashi had been deployed for the purpose it was created – to put down pro-democracy protests similar to those that successfully swept post-Soviet Ukraine and Georgia in 2004 and 2005.

Boris Nemtsov, a veteran liberal opposition leader and former deputy prime minister, was among those arrested in Moscow on Tuesday. A further 150 people were reportedly arrested during a similar protest in St Petersburg.

A Moscow court also announced it had sentenced Alexey Navalny, a popular anti-corruption activist, to 15 days' jail for disobeying police orders, after his arrest at a demonstration on Monday. Navalny has become the de facto leader of the movement against Putin and United Russia. Opposition leader Ilya Yashin was also sentenced to 15 days earlier in the day.

Russia's parliamentary election has been marred by allegations of violations and fraud. Politicians from two opposition parties, Yabloko and Just Russia, came out to support the protesters in Moscow and at least two were briefly detained.

"I am outraged at the lawlessness that we saw on 4 December, with the false elections, and on 5 December," said Yabloko leader Sergei Mitrokhin, whose liberal party failed to make it into the Duma, or Russian parliament. "I am ready to call for the entire government, headed by Putin, to resign."

Earlier in the day protesters had refused to leave Triumphal Square. Alexander Khonenko, 30, a small businessman and avid internet user, was typical of the crowd. "The atmosphere in Russia has changed," he said.

"Things are different now," another protestor, Ilya, 26, said. He was one of many who went to the square after learning of the protest there on Monday which gathered up to 8,000 people in the largest liberal protest yet against Putin's rule.

The Kremlin reacted harshly to the public challenge. Thousands of police and interior troops, alongside arrest lorries and water cannons, were stationed around Moscow on Tuesday. Among those deployed was the interior ministry's Dzerzhinsky division, named after the notorious founder of the KGB, which focuses on suppressing mass protests.

"Because of permitted mass gatherings and to prevent possible attempts at unauthorised gatherings, the total number of mobile reserves has been increased, including interior troops," a police spokesman told the Itar-Tass news agency.

The Kremlin also organised several protests by United Russia and pro-Kremlin youth groups in a bid to drown out the protests against Sunday's vote. The discontent has received no coverage on state-run television.

"We don't want a revolution," said an activist from Nashi offshoot Stal, who marched through Moscow earlier in the day and gave his name as Rauf. "We believe in our future – the election was clean."

Ilya Ponomaryov, a Duma deputy with the Just Russia party, was detained twice and repeatedly manhandled by riot police. "I hope this movement will only grow further," he said. "We will be victorious."

Ponomaryov said he refused to recognise the results of the parliamentary vote, which saw his party enter government thanks largely to many protest votes against United Russia.

He denounced the Kremlin's harsh crackdown on protests. "They are heating things up themselves – if before people thought they could influence things through the parliamentary route, now they're showing us that this way is impossible," he said. "If before people shouted that the government should resign, now they're shouting that [the government] should sit in jail," he said.

Putin has not commented on the protests, but met members of United Russia to acknowledge the party's loss of support. United Russia gained just under 50% of the popular vote, despite allegations of mass fraud, and lost 77 seats in the Duma.

"[These losses] are inevitable for any political force, particularly for the one which has been carrying the burden of responsibility for the situation in the country," Putin said.

"In today's conditions, the [election] result is good. We see and know what's happening, and it seemed not long ago at all that in countries with a more stable economy and social sphere, millions of people go out into the streets," he said.

Putin has in the past credited the party and government with preventing the sort of protests that gripped parts of the eurozone as the financial crisis worsened.

He appeared to directly address the popular nickname that Navalny coined for United Russia – "the party of crooks and thieves". "They say that the party of power is a party linked with theft, with corruption," Putin said. "If we remember the Soviet years – who was in power then? Everyone called them thieves and corrupted."

Discontent has been growing since Putin announced in September that he planned to run for the presidency in the country's presidential vote next March. Last month he was publicly booed at a sporting event, revealing the cracks in his image as Russia's all-popular "national leader". Although he still remains Russia's most popular politician, his ratings have plunged amid decreasing living standards and rampant corruption.

Russia's youth, born in the waning days of the Soviet Union or just after, have expressed dismay at the prospect of his returning to the presidency for two more six-year terms, which would put him in power until 2024. "I think that currently he is not a legitimate leader," said Sergei, 23, a lawyer protesting. "I want to hope things can change, that things can build up little by little until the presidential election."

Many protesters said they showed up after hearing about the spontaneous protest via the internet. LiveJournal, Russia's preferred blogging platform and a key site of discussion in a country dominated by state-controlled media, was inaccessible because of a distributed denial of service attack. Similar attacks crippled liberal media ahead of Sunday's vote.