The former prime minister and candidate for next month's snap Ukrainian presidential elections spoke with RFE/RL's Ukrainian Service in Kyiv on April 15.
"What is taking place today in Ukraine's east and south is not just an aggression, not just a terrorist act by Russia against those regions of Ukraine," she said. "I am sure that it has to be defined by a proper word: a war, which has been launched by the Russian Federation against Ukraine, and which has a goal to actually seize Ukraine's territory."
Tymoshenko called on authorities to "immediately announce a state of emergency" in Ukraine's eastern regions, where pro-Moscow protesters have seized government buildings and security headquarters in around 10 towns and cities.
Tymoshenko backed the creation of "brigades of territorial self-defense" forces in Zaporizhzhya Oblast, Dnipropetrovsk Oblast, and Kharkiv Oblast.
"In the nearest hours, we will recommend the appointment of the commanders of those territorial brigades of defense, who will be mobilizing people," she said.
She also said it was necessary to start a broad dialogue with the "elites" of the eastern region -- even if, she said, they are being "paid" by the Russian military and security agencies to stir up separatist sentiment and seize territory.
Russia sent forces into Ukraine's Crimea and annexed that territory in March.
Moscow has denied Ukrainian and Western allegations that Russia has also sent operatives into Ukraine's mostly Russia-speaking east to prepare for a possible military intervention.
Tymoshenko acknowledged the challenges faced by Ukraine's army, police, and special services, saying they have been left in "an extremely weak" and "demoralized" condition after years of mismanagement during the past two decades of Ukraine's post-Soviet economic decline.
Tymoshenko added that the crisis should not force the postponement of the May 25 presidential election.
Tymoshenko was convicted of abuse of power and sentenced to seven years in prison during the government of ousted President Viktor Yanukovych, who defeated Tymoshenko in the 2010 presidential election runoff. Tymoshenko's supporters said the prosecution was politically motivated.
Tymoshenko was freed in February under legislation passed by parliament as Yanukovych's pro-Russian government collapsed under the pressure of mass protests and clashes between demonstrators and security forces.
When she was prime minister, until spring 2010, Tymoshenko had a working relationship with Russian President Vladimir Putin.
But as mass demonstrations against Yanukovych's regime gained momentum last year, she intensified her calls for Ukraine to pursue a pro-Western course and integrate with the European Union.
In a recording of a private telephone call that was leaked in March, Tymoshenko was heard using coarse language to refer to Russians and saying all Russians on Ukrainian territory should be killed with an atomic weapon.
Tymoshenko acknowledged on Twitter that the phone call was real, but said the content was edited to make her words appear virulently anti-Russian.
Tymoshenko and billionaire businessman Petro Poroshenko are regarded as the frontrunners for the May 25 presidential election.