MOSCOW (Reuters) - President Vladimir Putin steered Dmitry Medvedev into the chairmanship of Russia's ruling party on Saturday and demanded reforms to the flagging organization he will rely on to keep his grip on the country's far-flung regions.
At Putin's behest, delegates at a United Russia congress elected Medvedev chairman with a unanimous show of hands, the final step in a choreographed role reversal the longtime leader hopes will preserve his rule against growing opposition.
After four years of playing No. 2 to his protege - when Putin was premier and led the party while Medvedev was president - the assertive performance by Putin on Saturday cemented his return to dominance as a single leader pulling the strings of power.
The event capped a series of moves to assert his authority over both security policy and the economic issues that are traditionally the province of the prime minister, the job Medvedev was given a day after Putin's May 7 inauguration.
Putin stole the show at a ceremony that formally celebrated Medvedev, hinting he ultimately remained United Russia's leader despite stepping back from formal ties with the party.
"I consider the United Russia party my key ally and partner - a force that is prepared to use all its opportunities to build a free, strong and thriving country," said Putin, 59, signaling continued support to a party that has been wary of Medvedev.
But he warned party members they must adapt to changing circumstances.
"Radical renewal is a serious challenge that will demand colossal work and commitment," said Putin, who helped United Russia achieve pervasive power nationwide during his 2000-2008 presidency and led it for most of Medvedev's 2008-2012 term in the top job.
The congress had a familiar mix of populism and pomp that has marked party meetings during Putin's 12 years in power.
But rousing rhetoric from both men was colored by obvious concern about the standing of United Russia, whose image was badly tarnished by widespread suspicions of fraud in a December vote that also drastically reduced its majority in parliament.
The party must "hear and feel the needs of society ... and broaden citizens' participation in governing the country," Putin told the congress, televised live from a meeting hall just outside the Kremlin.
"United Russia will set new standards for openness in political work."
United Russia emerged from the December 4 election with only a slim majority in the State Duma despite the fraud allegations, which spread on the Internet and fuelled the biggest opposition protests of Putin's rule.
The election deepened many Russians' feelings of powerlessness in a country dominated by Putin and United Russia.
With opponents looking to local elections and issues as a chance to gain a foothold after years at the political margins, Putin needs United Russia to maintain its hold on power in the disparate regions of the world's largest country.
Medvedev, speaking before the vote whose outcome was never in doubt, reiterated proposals to improve the party's "internal democracy", chiefly by holding competitive votes within the party to choose its candidates for regional and local elections.
Putin won the presidency by a comfortable margin despite the protests, which were also fuelled by dismay among some Russians at his Kremlin return.
United Russia has always been less popular than Putin himself and opposition leaders have capitalized on scandals and public perception of corruption among the ruling elite.
"Any signals of incompetence or corruption among officials who are United Russia members should be met with the harshest party decisions," Putin said. "The party must not tolerate those who violate justice or the dignity of citizens."
Putin firmly rejected one of the main demands put forward at the protests in Moscow and other cities this winter - to throw out the results of the December vote and hold a new parliamentary election.
The next State Duma vote is not due until late in 2016, but Putin's opponents hope to challenge United Russia in municipal votes and field candidates in elections for regional governors - some of them this autumn - while mounting more protests.
Putin may look to the party's performance as a test of Medvedev, 46, whose longevity as prime minister could hinge on the ability of the ruling apparatus to preserve political stability and withstand economic challenges.
Putin placed loyal figures in key economic posts in Medvedev's government last week and further undermined the cabinet's clout by bringing members of his own former government to potentially powerful advisory posts in the Kremlin.
Despite Putin's call for change within United Russia, critics say the appointments he has made suggest he has little real appetite for economic and political reforms they argue are needed if Russia is to remain stable.
The former Soviet KGB officer finalized the makeup of the influential presidential Security Council on Saturday, leaving in place a core of trusted allies from intelligence and security services who have been with him since his rise to power.
Additional reporting by Vladimir Soldatkin and Maria Tsvetkova; Editing by Andrew Heavens