KIEV, Ukraine (AP) — Former Prime Minister Yulia Tymoshenko said that Ukraine "must be a member of NATO" in order to protect itself from Russian aggression.

Tymoshenko, who is running in the May 25 presidential election, told The Associated Press in an interview Saturday that while only a minority of Ukrainians supported NATO membership previously, Russia's aggressive actions in the country's east had forced a "fundamental change" in public thinking.

"With his war against us, Putin was able to change the mentality of Ukrainians and turn us in a different strategic direction," she said, referring to Russian President Vladimir Putin. "In this case, NATO is the best choice for Ukraine."

The 53-year-old Tymoshenko and her blonde-braided halo rode to office on a wave of pro-democratic sentiment after the 2004 Orange Revolution. But her ratings in the election polls remain low, as Ukrainians remain skeptical about her political leadership and her occasional cooperative dealings with Putin in the past.

Tymoshenko spent two-and-a-half years in prison after being jailed for abuse of office, charges the West say were politically motivated by former President Viktor Yanukovych, who fled office in February following months of street protests. Tymoshenko says she suffers from severe back pain, and gave a fiery speech to protesters upon her release from prison in a wheelchair.

But like many of her Ukrainian colleagues, Tymoshenko, who hasn't previously backed NATO membership publicly, has ramped up the tough rhetoric as pro-Russia militias have seized police stations and government buildings in at least 10 cities across eastern Ukraine.

Ukraine and some Western countries have accused Russia of using covert forces to spur unrest in Ukraine. Acting Prime Minister Arseniy Yatsenyuk warned on Friday that Russia "is keen to start World War III," though Tymoshenko shied away from that assessment.

"I don't believe he will launch a third world war," said Tymoshenko. "I think he is merely blackmailing the world, understanding that the world will not allow World War III, and under this cover he is pursuing unlawful and aggressive deeds."

Tymoshenko said she welcomed another round of sanctions on Russia, and hoped they would be "so powerful that Putin will stop his aggression and return to the territory of his own country."

The U.S. and other nations in the Group of Seven said in a joint statement released Friday by the White House that they planned an additional round of economic sanctions on Russia in response to its actions in Ukraine.