KIEV, Ukraine -- Former Prime Minister Yulia Tymoshenko, one of Ukraine's most popular and resilient politicians, has announced her presidential bid.

Opinion polls have consistently placed the 58-year-old, who was the country's prime minister between 2007 and 2010, as a front-runner in the presidential election set for March 31, ahead of incumbent Petro Poroshenko.

Tymoshenko announced her bid to a rapturous audience at her party congress in Kiev on Tuesday, promising to regain control of the Russian-annexed Crimean peninsula and the separatist-held areas in the east. She assailed Poroshenko and top officials for profiting from the ongoing separatist conflict in the east.

"I can promise you I will not be treating the war as a profitable business," she said.

Tymoshenko was first elected to parliament in 1996 and spearheaded massive protests in 2004 together with then-presidential candidate Viktor Yushchenko. Following Yushchenko's victory, Tymoshenko was appointed prime minister. She was dismissed less than nine months later amid disputes with Yushchenko. She served as prime minister again between 2007 and 2010.

Tymoshenko spent two-and-a-half years in prison for signing a gas deal with Russia, which was largely viewed as retribution by her political rival, then-President Viktor Yanukovych. Tymoshenko narrowly lost to Yanukovych in the 2010 presidential vote and to Poroshenko in 2014. Poroshenko has not formally announced his bid for re-election yet.

Tymoshenko, originally from the Russian-speaking east of Ukraine, has been positioning herself as a pro-NATO, pro-European Union candidate and a supporter of the troops who are fighting Russia-backed separatist in the industrial Donbass region. At the start of her two-hour speech she invited on stage several dozen veterans of the conflict in the east, some of whom served in the grueling battle for the Donetsk airport.

Among other prominent figures who have endorsed Tymoshenko are Patriarch Filaret, leader of one of the split Ukrainian churches, and former Georgian President Mikheil Saakashvili, who served as governor for the Black Sea region of Odessa.