A lawyer for Ukraine's jailed former prime minister, Yulia Tymoshenko, says she has started a hunger strike after prison guards beat her.

Tymoshenko, who has a severe spinal condition and needs hospital treatment, was taken last week to a clinic in the eastern city of Kharkiv where her jail is located, but was returned to prison a day later after refusing treatment.

Her lawyer, Serhiy Vlasenko, said on Tuesday that prison officials kicked her in the stomach while taking her to the hospital by force.

Prison authorities declined to comment.

The west has condemned Tymoshenko's seven-year sentence for abuse of office as politically motivated.