Russian Prime Minister Vladimir Putin responded to an election setback and protests by promising on Tuesday to reshuffle the government next year but his spokesman warned the opposition that any unsanctioned rallies would be stopped.
Under pressure after his party won only a slim majority in parliament on Sunday and the opposition staged its biggest protest in Moscow for years, Putin said the government had to do more to respect the people's demands for modernization.
"There will be a significant renewal of personnel in the government," he told members of his United Russia party.
It was a first overt sign of concern in the upper echelons of power over the election, which loosened United Russia's grip on the State Duma lower house and signalled growing weariness with Putin's 12-year rule, economic problems and corruption.
But he promised no immediate changes -- the reshuffle would be after a March 4 presidential election he is expected to win -- and his spokesman Dmitry Peskov made clear police would prevent protesters staging rallies without official permission.
"Those who hold sanctioned demonstrations should not have their rights limited in any way -- and that is what we are observing now," Peskov said.
But he added: "The actions of those who hold unsanctioned demonstrations must be stopped in the appropriate way."
Witnesses said up to 5,000 people joined Monday's protest to complain against alleged electoral fraud and demand an end to Putin's rule.
They planned a new rally to press their demands on Tuesday evening, despite the lack of permission from the authorities and a heavy police presence in the capital.
About 300 people were detained in Monday's demonstration and police issued a statement on Tuesday saying they would not permit any "provocations" -- a clear warning to the protesters.
A Moscow court sentenced Ilya Yashin, one of the organisers on Monday's rally, to 15 days in detention but he told reporters: "Of course we will continue protesting."
"This is no doubt a political decision aimed at intimidating me and my colleagues. We are not going to stop our struggle," he said, adding that his verdict could "arouse even bigger discontent among the people."
WARNING OF ARAB-SPRING STYLE REVOLT
United Russia is set to have 238 of the 450 seats in the State Duma, 77 fewer than the 315 seats it won in 2007.
This has little practical impact because United Russia can even muster the two-thirds majority needed for constitutional changes if it forges alliances with other parties.
But the vote points to a change of mood in Russia after years of domination by the former KGB spy and his party, which no longer has quite such an air of invulnerability.
European monitors also said the election had been slanted in United Russia's favour. U.S. Republican Senator John McCain went further, warning on Twitter: "Dear Vlad, The Arab Spring is coming to a neighborhood near you."
Many Russian political experts have dismissed suggestions that Putin could face an uprising in a country which has little tradition of major street protests, despite the 1917 Bolshevik Revolution, and dissent has often been crushed.
But Putin's popularity ratings, although still high, have fallen this year and he upset many Russians by saying he planned to swap jobs with President Dmitry Medvedev after the March presidential election, opening the way for him rule until 2024.
(Writing by Timothy Heritage, Editing by Steve Gutterman)