Ukraine was forced to postpone the Central European summit after leaders of Germany, Latvia, Estonia, Austria, Italy and the Czech Republic threatened not to show up. The leaders accused Ukraine of poorly handling Tymoshenko's fragile medical condition.
Foreign Ministry spokesman Oleksandr Dykusarov said Ukraine plans to hold the summit at a later time.
"Ukraine decided to postpone the summit and not to hold it on May 11-12 in Yalta," Dykusarov told Russia's RIA Novosti news agency. "The event will be held at a later time that will be determined through diplomatic channels."
Tymoshenko's treatment during her time in Kachanivka women's penal colony No. 54 in Kharkov has been a source of controversy, since photos circulated last week of her covered in bruises she said were inflicted by prison guards.
Tymoshenko, 51, is serving a seven-year sentence after being convicted last year of abuse of office. RIA Novosti reported Western governments have called Tymoshenko's trial politically motivated.
The Ukrainian News Agency said Tymoshenko will be moved to Ukrzaliznystia Central Clinical Hospital for in-patient treatment for severe back pain caused by a herniated spinal disc.