A lawyer for Ukraine's jailed former prime minister, Yulia Tymoshenko, says she has been on a hunger strike since allegedly being beaten up by prison guards last week.

Serhiy Vlasenko said Tuesday the guards beat up Ms. Tymoshenko while while moving her to a hospital on Friday. He said her arms and stomach are still bruised from the incident.

Prosecutors admit she was taken to a hospital against her will, but deny allegations she was beaten.

Ms. Tymoshenko has complained of severe back pain and has asked for medical treatment.

The opposition leader was sentenced to seven-years in jail last year on charges of abuse of office in a 2009 gas deal with Russia. She is now standing trial on tax evasion charges that could extend her jail time to 12 years.

She denies the charges and argues they are part of a campaign by current Prime Minister Viktor Yanukovych to remove his strongest political rival.

The United States, the European Union and human rights groups have condemned the charges against Ms. Tymoshenko as politically motivated.