(Updates with details of the rally, quotes) By Margarita Antidze TBILISI, Sept 28 (Reuters) - Up to 15,000 opponents of Georgian President Mikhail Saakashvili jammed central Tbilisi on Friday to protest at the arrest of an ex-minister who accused Saakashvili of corruption and plotting to kill a businessman. Protesters shouting "Long live Georgia!" and "New president!" pushed back police lines and stopped traffic at Rustaveli Avenue to flood the space in front of parliament. "The main question today is: them or us," Goga Khaindrava, a former member of Saakashvili's cabinet who joined the opposition, told the cheering crowd. "We came here to stay, they will have to go," he added. The rally was the biggest anti-government protest since Saakashvili, a U.S.-educated lawyer, came to power in this ex- Soviet state in a peaceful revolution in 2003. His government quickly became the darling of Western capitals with its pledges of economic reform, pursuit of NATO membership and harsh criticism of former imperial master Russia. There was no reaction to the protests from the government or from Saakashvili, who has been in New York attending the U.N. General Assembly and planned to travel onwards to Greece. About 20 buses with police in full riot gear were gathered at a remote part of Rustaveli Avenue, but there was no immediate indication they were preparing for action. Opposition parties called the protest after the arrest Thursday evening of former defence minister Irakly Okruashvili, a long-time ally of the president who was sacked last year. Two dozen police in camouflage broke into his political headquarters, dragged him away and searched the premises. The arrest came two days after Okruashvili, a hawk who wants Georgia to recover two pro-Russian separatist regions by force, unleashed a stinging attack on Saakashvili. Without producing evidence, he accused the president of presiding over massive corruption and ordering the elimination of a prominent businessman. The government press office did not react, although a close aide said the charges were "baseless". Opposition leaders described Okruashvili's arrest on charges of money laundering and abuse of power as the "start of political terror" in Georgia. UNITING OPPOSITION Ahead of Friday's rally, a leading parliamentary ally of Saakashvili warned demonstrators that police could use force if the protest turned violent. "If the opposition uses violent methods to attack the authorities, then we will reply with force," Giga Bokeria said. Saakashvili sacked Okruashvili, a member of his inner circle, in 2006 at a time when Tbilisi was under heavy pressure from the West to tone down its bellicose statements because of fears that conflict with Russia might escalate into war. Okruashvili had attacked Russia for propping up the separatist regions of South Ossetia and Abkhazia and promised military action to re-establish Tbilisi's control there. Okruashvili joined the opposition and set up his party this year after several allies were arrested on corruption charges. Georgia is due to hold simultaneous parliamentary and presidential elections towards the end of next year. Saakashvili's opponents are mostly weak and have so far posed no political threat to him. But analysts say that Okruashvili has been gaining political weight in the past few months and could turn into a powerful political figure. Friday's protest united the often fractious opposition parties, providing an outlet for citizens frustrated by Georgia's continuing problems. "I came here to protest against the authorities rather than to defend Saakashvili," said protester Maya Areshidze. Media in Russia, whose government has heavily criticised Saakashvili's overtures to the West, reported enthusiastically on "political chaos" in Georgia, playing up the accusations against the president.
