Thousands of people demonstrated in Georgia on Friday against the arrest of a former minister, in the most serious challenge yet to the authority of pro-Western President Mikheil Saakashvili. Irakli Okruashvili, a former defence minister, was arrested on corruption charges on Thursday shortly after alleging that Saakashvili had ordered the killing of high-profile figures. The allegations were dismissed by officials as "baseless and untrue." Thousands rallied on Friday in the capital Tbilisi to denounce the arrest. Organisers said up to 10,000 people had come out, although an AFP reporter on the scene and local news agencies put the number closer to 5,000. Organisers vowed after demonstrators dispersed to continue protests in the coming days. Saakashvili has touted his government`s democratic record as he pushes for Georgia`s entry into NATO and the European Union. But Okruashvili, who also supports integration with the West, appeared determined to counter Saakashvili`s clean-cut image. In a note read out to the crowd by lawmaker Koka Guntsadze, a political ally, Okruashvili said: "Be united. Fight to protect your rights. Fight by all legal means to escape from this tyrant." The ex-minister`s supporters accused the president of trying to silence a potential rival. Okruashvili heads the Movement for United Georgia party. The arrest took place against the backdrop of rising tensions between Georgia and Russia, as well as violence in two separatist regions. Giorgi Khaindrava, a former senior minister who was fired last year, said the arrest showed Georgia was in a political crisis. "A criminal organisation led by Saakashvili is in power," he said. "The only solution would be the resignation of the president, the dismissal of parliament and early elections." But Giga Bokeria, a senior official in the ruling National Movement party, defended Okruashvili`s arrest, saying "neither former officials nor acting ones... are above the law." Okruashvili was charged with extortion, money laundering, abuse of power and negligence during his time as minister. Video footage released by prosecutors on Friday showed Dmitry Kitoshvili, a former presidential spokesman recently charged with extortion, confessing that he and Okruashvili had forced a local businessman to sell them 10 million dollars (seven million euros) worth of shares in a local telecommunications company for a knock-down 250,000 dollars (176,000 euros). Saakashvili fired Okruashvili last year after the minister made hawkish statements on the return of two Russia-backed separatist regions, Abkhazia and South Ossetia, to Georgian control. Okruashvili re-emerged this week with an announcement he was forming an opposition party and that the president had ordered him to kill prominent public figures including a top businessman. He produced no evidence to support his allegations. Saakashvili, who was in New York for the UN General Assembly, has not responded to the accusations. Okruashvili had been in Saakashvili`s inner circle since before the mass protests of the 2003 Rose Revolution propelled Saakashvili to power. He also served as prosecutor general and interior minister. Georgia is to hold presidential and parliamentary elections next year and analysts said Okruashvili has the credibility and power base to pose a threat to Saakashvili in the polls. Saakashvili has cultivated close ties with Western countries, in particular the United States, which has provided substantial economic and military aid to the small mountainous state on Russia`s southern border. Georgia`s pro-Western aspirations have infuriated Moscow, which has cut travel links with Georgia and imposed a ban on key Georgian exports.