German doctors who traveled to Ukraine to examine the jailed and ailing ex-Prime Minister Yulia Tymoshenko say that she agreed to treat her back condition at a local hospital.

Dr. Karl Max Einhaupl said the treatment of Tymoshenko's herniated disk will start Tuesday.

The 51-year-old Tymoshenko is on a hunger strike to protest the prison's alleged mistreatment of her as she serves a seven-year sentence on charges of abusing her powers when she was prime minister.

Critics have described her case as politically motivated. They charge that Ukrainian President Viktor Yanukovych, Tymoshenko's rival in the 2010 presidential election, orchestrated her prosecution. Government officials have denied any claims of bias in the case.

Tymoshenko's aide Alexander Turchinov on Friday raised alarm about the former premier's health. "She's been on a hunger strike for 15 days," he said. "Her life is in real danger."

The Ukrainian Penitentiary Service confirmed the visit by the German doctors in an online statement but did not provide details. It mentioned that Tymoshenko's daughter and lawyer were not allowed to see her on Friday because of the doctors' visit.

Tymoshenko's allies were not informed of the visit in advance.

German doctors from the Berlin-based Charite clinic also traveled to Ukraine last month to examine Tymoshenko and concluded she was in urgent need of specialized care.

German Chancellor Angela Merkel urged Kiev on Thursday to allow Tymoshenko "proper treatment" for her ailments, saying she could come to Germany for medical care.

Russian President-elect Vladimir Putin also offered help, suggesting that Russia would welcome Tymoshenko to be treated at any hospital in Russia.

Putin was Tymoshenko's counterpart in signing a 2009 natural gas export deal that landed the Ukrainian politician in jail. Although Putin has stopped short of standing up for her, he has said that there could not have been any violations of the law in the agreements they both signed.

On Thursday, European Union President Herman Van Rompuy announced he would not travel to any of next month's Euro 2012 soccer tournament matches in Ukraine in protest at Tymoshenko's treatment, joining other top officials such as European Commission President Jose Manuel Barroso and the governments of Austria and Belgium.