MOSCOW - Hundreds of people took to the streets of Moscow for a second successive day on Tuesday to demand an end to Vladimir Putin's 12-year rule, defying a crackdown by tens of thousands of police reinforced by crack Interior Ministry troops.

Activists of Pro-Kremlin youth movements take part in a demonstration as a response to the protest rally against the results of the parliamentary elections and the policies conducted by Russian authorities, in Moscow Dec 6, 2011. [Photo/Agencies]?

Police said they had detained about 250 people in central Moscow when they tried to stage an unapproved rally and held about 200 more in St Petersburg, where opposition forces have also been emboldened by the prime minister's worst election setback since he took power in 1999.

After permitting the biggest opposition rally in Moscow for years on Monday evening, the police were out in large numbers. The Interior ministry said about 2,000 special troops were supporting almost 50,000 police, and some moved through the city centre in armoured vehicles in a show of force.

Hundreds of pro-Putin youths also tried to spoil the rally, shouting "The people! Putin" and beating drums to drown out the opposition protesters' chants of "Russia without Putin" and "We want free elections!" A few minor scuffles broke out.

Boris Nemtsov, a liberal opposition leader, told Reuters he had been detained. Two opposition figures, blogger Alexei Navalny and Ilya Yashin, were jailed for 15 days for their role in Monday's opposition protest, the biggest in Moscow for years.

"We are not going to stop our struggle," Yashin said.

"We want fair elections. Look at what they have done to our country, our Russia," said a man who gave his name only as Alexei as he was pushed by riot police into a waiting bus.

The organisers used social media such as Twitter and Facebook to attract new support from people who no longer consider Putin to be invincible.

"I had to come out today because I can't stay quiet about how they just spit on us," said Mikhail Torupov, a Muscovite who said he had hardly ever protested before.

Policemen detain an activist during a rally to protest against the results of the parliamentary elections and the policies conducted by Russian authorities in Moscow Dec 6, 2011. [Photo/Agencies]?