Ukrainian opposition leader Yulia Tymoshenko says she plans to run for president in 2019, setting up a possible showdown with incumbent Petro Poroshenko.

In a video conference on her Facebook page on June 20, Tymoshenko said she will run for the presidency "not just to play an authoritarian game…but to lift Ukraine back on its feet."

"The presidential office for me is not a PlayStation, but a place to introduce real changes our country has been longing for," said Tymoshenko, who is leader of Ukraine's opposition Batkivshchyna (Fatherland) party.

Tymoshenko added that she would initiate a referendum on a new constitution if she was elected president.

"I will propose a new constitution for Ukraine to make it a real public agreement between the government and the people in order to de-monopolize the powers of the authorities," she said.

"On one hand, the authorities will be more able to implement strategic changes. On the other, they will become properly organized, balanced, and controlled by society," she added.

She said that parliamentary elections, scheduled for the autumn of 2019, must be conducted under the rules of the new constitution.

Meanwhile, Tymoshenko said she will never give up the fight to have Crimea and Ukraine's eastern regions brought back under Kyiv's control.

Ukraine's Crimea Peninsula was seized and annexed by Russia in 2014. Moscow has also supported separatists fighting a bloody war in eastern Ukraine that has killed more than 10,300 people.

Tymoshenko, 57, lost to pro-Russian candidate Viktor Yanukovych in 2010 and to Poroshenko in 2014 after Yanukovych was driven from power and fled to Russia.

Tymoshenko, who was Ukraine's prime minister from 2007 to 2010, was jailed on embezzlement charges following her government's defeat by Yanukovych in 2010.

Her sentence was viewed by much of the international community as political in nature. She was released in February 2014 and later reelected to parliament.

According to recent polls, Tymoshenko and Poroshenko each have support of 14 to 16 percent of Ukrainian voters.