Supporters of former Ukrainian prime minister Yulia Tymoshenko on Saturday started an indefinite sit-in to protest her detention as European capitals expressed concern over her dramatic arrest. A Kiev court Friday placed the glamorous Tymoshenko under arrest for contempt of court in her ongoing trial on charges of abuse of power, which she claims is a vendetta pursued by her rival, President Viktor Yanukovych. In extraordinary scenes, the opposition leader was driven through central Kiev's Kreshchatyk avenue in a prison van surrounded by hundreds of police to the Lukyanovsky detention centre in Kiev where she spent the night. At least 100 supporters, including parliament deputies, have now pitched a line of some 30 tents on Kreshchatyk avenue near the courthouse and vowed to maintain their sit-in until Tymoshenko is released. "Freedom to political prisoners!" "He (Yanukovych) turned the country into a prison", were among the slogans brandished by the demonstrators. Tymoshenko's right-hand-man Olexander Turchinov meanwhile warned of a repeat of the 2004 Orange Revolution uprising in Kiev's Maidan square that brought a pro-Western government to power. He said that if people turned out in force in the streets, "already in September, Ukraine could have a true government of the people." Tymoshenko, one of the leaders of the Orange Revolution, narrowly lost to her old rival Yanukovych in presidential elections last year. The presidency has denied any involvement in her trial. Ukraine's human rights ombudswoman Nina Karpacheva visited Tymoshenko late Friday and said she was being kept in a cell with one other woman and would be allowed a television and refrigerator if relatives sent them. Tymoshenko's allies released a video address recorded a day before her arrest in which she predicted her detention. She vowed to protect Ukraine and not to seek asylum abroad. "Be sure -- they will never break me," she said. France said it has concerns over the motivations of the trial while EU foreign policy chief Catherine Ashton said the events were "a cause for concern about the state of the rule of law in Ukraine." Sweden's Foreign Minister Carl Bildt was even blunter, saying the trial was an "embarrassing spectacle which "does great damage to a great country." Meanwhile, politically-committed Ukrainian boxing star Vitali Klitschko said he halted training for an upcoming world championship fight to return to Kiev and take part in a "battle for democratic values" following the arrest of Tymoshenko. Tymoshenko is accused of causing a loss to Ukraine's budget of 1.5 billion hryvnias ($190 million) when she signed a new energy contract with Russian Prime Minister Vladimir Putin after a brief interruption of gas deliveries in 2009. Friday's drama coincided with a court appearance by Ukrainian Prime Minister Mykola Azarov, who gave witness testimony backing the prosecution and was promptly described by Tymoshenko as a "fully-certified, corrupt old man". This comment appeared to trigger the court's order to arrest Tymoshenko, who since the trial started in June had irritated youthful judge Rodion Kireyev by mercilessly mocking him on Twitter. "I advise no-one to mock the court, as the court is one of the foundations of our state," Azarov said Saturday, according to the Interfax-Ukraine news agency. According to online newspaper Ukrainska Pravda, Tymoshenko built a friendly rapport with prison officials on arrival but had to let down her trademark knotted hair braid in line with the detention centre's rules. Known in Ukraine as the "Iron Lady" after her heroine ex-British prime minister Margaret Thatcher, Tymoshenko was also briefly imprisoned in 2001 on forgery charges that were eventually quashed. The current charges carry a sentence of between seven and 10 years in prison. Even a suspended sentence would disqualify her from parliamentary polls next year and the next presidential elections in 2015.