Georgian President Mikheil Saakashvili on Wednesday promised to punish those responsible for torturing and raping prisoners in a video shown on television, which triggered protests in the capital, Tbilisi.
The government said guards had been paid to stage the abuse for political motives, less than two weeks before a parliamentary election.
The prosecutor's office said 10 people had been arrested, including the head of the Tbilisi prison, two deputies and a number of guards. The prisons minister said she was resigning.
"Tonight, I tell all the victims of these inhuman actions and the whole nation that the Georgia we have built and we are all building together shall not and will not tolerate such behavior — in its prisons or anywhere else," Saakashvili said in a statement issued in the early hours of Wednesday.
"Those who committed these crimes will spend long years in jail, as will those who bribed guards to stage these horrors and film them," he said, promising that the rights of prisoners would be better protected.
Georgia, a key transit route for oil and gas supplies across the volatile Caucasus region, is gearing up for an Oct. 1 election, in which Saakashvili and his United National Movement face a challenge from a new opposition coalition, Georgian Dream, led by billionaire entrepreneur Bidzina Ivanishvili.
Hundreds of demonstrators rallied overnight in the capital after two pro-opposition television channels, including one owned by Ivanishvili, aired the footage purporting to show torture, rape and other abuses in the Tbilisi prison.
"This bloody regime should step down," said Dachi Tsaguria, one of the organizers of the protest.
The protesters, who were urged to join the rally by messages on Facebook, held posters saying "Rape me!"
Dozens of people began gathering in the center of the capital to resume the protest Wednesday.
The government said the videos had been staged and recorded by police officers who had been bribed by "politically motivated persons."
"An investigation revealed that several members of the jail's security department had been involved in a plan to carry out abusive activities and record them," the Interior Ministry said in a statement.
"Evidence shows that payments were made to coordinate and stage these appalling activities," it said.
Georgian Dream, which unites several opposition parties, has generated large turnouts at its rallies, although most opinion polls show that it trails the ruling party.
Ivanishvili has a fortune estimated by Forbes magazine at $6.4 billion. He and other opponents accuse Saakashvili of curbing freedoms and criticize him for leading Georgia into a disastrous war with Russia in August 2008.