Georgian billionaire and opposition leader Bidzina Ivanishvili.
TBILISI, Sept 22 (Reuters) - Voters in Georgia face a stark choice between "good and evil" in parliamentary elections on Oct. 1, said opposition leader Bidzina Ivanishvili on Saturday, following days of protests over state prison brutality that have left the ruling party reeling.
"We should make a choice between good and evil on October 1," Bidzina Ivanishvili, told a crowd in Zugdidi in western Georgia.
"We promise to come to power and to restore justice," said the billionaire leader of the "Georgian Dream" opposition coalition.
Thousands of people gathered at Zugdidi's central square to show their support for the opposition, which poses a serious challenge to President Mikheil Saakashvili's United National Movement party's chances of winning the upcoming vote.
Protests were sparked in Georgia this week after footage showing the torture and rape of inmates in the capital's main prison was aired by two television channels supportive of the opposition.
Hours after the release of the prison video, Saakashvili promised to punish those responsible and seek radical reforms of the jail system, asking policemen to take over prison guard duties while reforms were being worked out.
The country's interior minister tendered his resignation over the scandal and the prisons minister also stepped down.
Surveys conducted before the scandal erupted showed Saakashvili's party some 20 points ahead of Georgian Dream, a platform set up by Ivanishvili.
Saakashvili's government says the video, which shows guards beating, punching and humiliating prisoners, as well as inmates being raped with objects, was recorded by guards who were bribed by "politically motivated persons".
The head of the Tbilisi prison, his two deputies and several prison guards were arrested, while international organisations and human rights groups called for a prompt investigation.
Ivanishvili, his fortune estimated by Forbes magazine at $6.4 billion, owns one of the broadcasters that showed the film.
A once-reclusive tycoon whose wealth equals nearly half Georgia's economic output, Ivanishvili launched his political movement last year and has campaigned on calls for Saakashvili to resign.
Saakashvili became the West's political darling when he rose to power after the bloodless "Rose Revolution" that toppled Eduard Shevardnadze, a former Soviet foreign minister, in 2003.
But opponents have accused him of curbing political freedoms and criticised him for leading Georgia - a country of 4.7 million people on a transit route for oil and gas supplies across the volatile Caucasus region - into a brief but disastrous war with Russia in August 2008.