Prime Minister Vladimir Putin, facing an outburst of protest against his rule, called Monday for an update of Russia's political system in response to what he said was a maturing civil society.

"We need to create a political system where people can and must speak the truth," Putin said in a wordy article which also quoted Soviet dissident writer Alexander Solzhenitsyn.

"Our civil society has become incomparably more mature, active and responsible. We need to update the mechanism of our democracy. They must fit in growing public activity," Putin said in the article published on his campaign website and in the business broadsheet Kommersant.

Putin said the middle classes had become more "demanding" of politicians.

"The new demands towards the authorities, the middle classes' emergence from their narrow world of building their own prosperity is the result of our efforts. We worked on this," he wrote.

In a rare acknowledgement of the role of the Internet, which has galvanised the opposition movement, Putin called for the parliament to be obliged to discuss any public petition that manages to gather 100,000 signatures on the Internet.

Putin is battling the worst legitimacy crisis of his 12-year rule.

Tens of thousands took to the streets since disputed December parliamentary elections in a wave of protests unseen since the early 1990s.

Opposition activists said more than 120,000 people braved frosty weather to attend an opposition rally on Saturday, the budding protest movement's third since December.

In the piece -- his fourth campaign article -- Putin stressed that direct elections of regional governors would be reintroduced, a system he eliminated under his presidency in 2004.

But at the same time he said Russia must avoid "the temptation to simplify politics, to create a fictitious democracy" and insisted the country needed a "strong, effective and respected federal centre."

Putin has written four articles since January on subjects including Russia's economy and illegal immigration, although he has refused to take part in debates with the other presidential candidates.