Yulia Tymoshenko to run for president – and take on Ukraine's 'Enemy No 1' Vladimir Putin

Widely expected announcement comes shortly after IMF agrees $18bn rescue package as interim PM warns of hard-hitting reforms

Yulia Tymoshenko to run for president (EPA)

Former Ukrainian prime minister Yulia Tymoshenko is set to run for president in the upcoming May elections.

Speaking at a press conference, Ms Tymoshenko said she would run as a "candidate for Ukrainian unity" and fight against corruption.

Ditching her princess hairstyle, she claimed none of the other candidates understand "the depth of the lawlessness gripping Ukraine" and insisted Russian president Vladimir Putin remains the "number one enemy".

Often regarded as a divisive figure, she promised to find a "common language" between her pro-European supporters and Russian-speakers, many of whom continue to back former President Viktor Yanukovich.

Mr Yanukovich was ousted by the Ukrainian parliament after more than three months of protests in February.

"I will be the candidate of Ukrainian unity," Ms Tymoshenko said. "The west and centre of Ukraine has always voted for me, but I was born in the east, in Dnipropetrovsk."

Earlier this week, Ms Tymoshenko was dragged intro fresh controversy after she appeared to suggest it was time to "take up arms and go wipe out" Russians "together with their leader" in a leaked telephone call broadcast on Russian state television.

She did not name Mr Putin by his name.

Ms Tymoshenko tweeted the conversation had been altered and apologised for using "expletives". She added: "Cheers to the FSB", referring to the Russian security service.

According to opinion polls, chocolate baron Petro Pororoshenko is leading the race for the presidency with the backing of 24.8 per cent of voters, followed by boxer turned politician, Vitali Klitschko with 8.9 per cent of the vote. Ms Tymoshenko is on third place with 8.2 per cent of the vote.

Ms Tymoshenko, 53, was released from prison in February following the ousting of her political nemesis Yanukovich. She was imprisoned in 2011 for abuse of office linked to a gas deal with Russia.

She rose to the forefront of Ukrainian politics during the 'Orange Revolution' that overthrew Mr Yanukovich's first administration in 2004. Ms Tymoshenko served twice as prime minister and ran for president in 2010, only to be narrowly beaten in a run-off vote by Mr Yanukovich.

The announcement comes just hours after the International Monetary Fund pledged a $14-$18 billion rescue package for Ukraine to help the country's acting government meet its debt obligations against the backdrop of Russian intervention.

The IMF deal is set to unlock support of $27 billion from various countries over the next two years, but it will come with strings attached, including serious austerity measures and higher energy prices.

In a statement, the IMF warned Ukraine is facing "difficult" challenges following the "intense economic and political turbulence of recent months".

In an address to the Ukrainian parliament, interim prime minister Arseniy Yatsenyuk warned Ukraine is teetering "on the brink of the economic and financial bankruptcy" and signalled more pain ahead.

Mr Yatsenyuk said new structural reforms, including raising taxes and a freeze on minimum wage, will hit families hard but he insisted the government had "no choice but the tell the truth".

On Wednesday, Ukraine announced a radical 50 per cent increase in domestic gas prices starting 1 May in an effort to secure the IMF bailout, which made scrapping energy subsidies a key condition for the deal to move forward.

The election is expected to take place on 25 May.