Ukraine's jailed opposition leader Yulia Tymoshenko began receiving back pain treatment in hospital on Saturday after missing the controversial opening of her new trial for tax fraud.
Witnesses cited by local media said two ambulances and four police cars arrived at the women's prison in the eastern city of Kharkiv where she is serving a seven-year sentence and took her away late Friday.
"Tymoshenko arrived at the Central Clinical Hospital (Friday) evening," the Ukrainian prison service said in a statement.
"After reviewing the conclusions of German doctors, Tymoshenko expressed a desire to begin treatment in the clinic that was proposed for her... in the city of Kharkiv," it said.
The flamboyant but divisive 2004 Orange Revolution leader was convicted of abuse of office for negotiating a gas deal with Russia while prime minister in 2009 that the new administration says was disadvantageous for Ukraine.
She was sentenced last October at the end of a high-profile trial watched closely by strongly critical diplomats from Europe and the United States.
The case cast a shadow over Ukraine's nascent relations with the European Union and prevented the signing of a partnership agreement the ex-Soviet nation hopes to secure before eventually winning membership in the bloc.
Western officials criticised the trial as selective justice while Tymoshenko has branded her prosecution as the result of a political vendetta being waged by her triumphant presidential rival Viktor Yanukovych.
But prosecutors have brushed aside the complaints and have since launched several new cases against Tymoshenko relating to her time in the 1990s as head of a private natural gas trading firm.
She went on trial again Thursday on tax evasion charges that may extend her sentence by five years. The 51-year-old sent a formal letter to the authorities saying she was in too much pain to attend.
The decision to move Tymoshenko to a local hospital represents a partial concession by both prosecutors and the former premier.
Ukraine's prison service has persistently denied the seriousness of her condition while members of the ruling party accuse of her of feigning pain to draw more Western sympathy and avoid the new trial.
Tymoshenko for her part had previously refused treatment in a Ukrainian hospital until it had been cleared by a team of visiting German doctors who examined her earlier this year.
A German doctor formally approved the clinic this week.
But Tymoshenko's attorney said he had "serious doubts" about whether Tymoshenko had actually agreed to be moved.
"She was moved at night, suddenly and right before the start of the weekend, when she will not be able to meet with her defence," court representative Serhiy Vlasenko told AFP.
"In the mean time, (Ukrainian health officials) can say anything they want."
Vlasenko added that the chief visiting doctor had given only his cautious approval of the clinic and had expressed scepticism about whether "therapy there would work."