Ukraine's former prime minister Yulia Tymoshenko, right, whose jailing last year has soured the former Soviet republic's relations with the West, has been moved to hospital where she is expected to receive treatment for back pain.

The imprisonment of Tymoshenko, 51, a fierce opponent of President Viktor Yanukovich, has become a key issue in Ukraine's relations with the European Union, which saw her prosecution as an example of selective justice. Tymoshenko, 51, who is now on trial on graft charges, has suffered back pain for months.