KIEV (AFP) - Ukraine's jailed ex-premier Yulia Tymoshenko, whom Parliament voted to free immediately on Saturday, is one of the country's most divisive politicians and a persistent thorn in the side of beleaguered President Viktor Yanukovych.

Tymoshenko, jailed for seven years on abuse of power charges in 2011, is a hugely polarising figure in Ukraine and has been a prominent pro-European voice in a country torn between rival allegiances to Moscow and the West.

She is loved by her supporters as an unflinching defender of Ukrainian sovereignty and its European future who was ruthlessly punished by Yanukovych for daring to challenge his power.

But for her detractors, Tymoshenko, 52, is an unscrupulous political opportunist with no fixed ideas who became enormously rich in the corruption-stained 1990s and deserves what she got.

A slender, telegenic blonde known for wearing her long hair in an elaborately braided crown, Tymoshenko's looks belie a steely temperament that has been compared to former British prime minister Margaret Thatcher's - one of her heroines.

Known at home as the "Iron Lady", after the late Thatcher, or simply by the Ukrainian word for "she" - "vona" - Tymoshenko was a leader of the 2004 Orange Revolution that forced the annulment of elections initially awarded to Yanukovych.

She challenged Yanukovych in a bitterly contested 2010 presidential election, losing in a run-off and then finding herself the target of a string of criminal investigations she claimed were aimed at eliminating her from politics.

She was first arrested in August 2011, then sentenced to seven years in October that year on controversial charges of abusing her power in a 2009 gas deal signed with Russia during her premiership.

Her jailing, which Tymoshenko argued was the result of a vendetta pursued by Yanukovych and his "family" of close relatives and oligarchs, prompted anger in the West and a crisis in Ukraine's relations with the European Union.

Seeking to burnish her credentials as Ukraine's number one champion of EU integration, Tymoshenko said her own fate should not stand in the way of Kiev signing an Association Agreement with the bloc.

When Yanukovych unexpectedly snubbed the deal on November 21 in favour of closer ties with Russia, members of her Batkivshchyna (Fatherland) party were at the heart of street protests that erupted and demands for her release remained vocal.

Over the next three months, pro-European demonstrators turned Kiev's iconic Independence Square into a battle zone, where fierce clashes between protesters and police have left dozens dead this week.

Even from her detention in a prison hospital - where she was moved due to serious back problems - Tymoshenko has played a role in the protests, urging the opposition to stay strong and oust her nemesis.

"The only subject of negotiation with Yanukovych is the conditions of his departure," she said in a recent interview with weekly Dzerkalo Tyzhnia.

As Yanukovych's regime appeared close to collapse after a peace deal was reached on Friday, Tymoshenko was back in the spotlight.

On Saturday, Parliament overwhelmingly voted for her to be immediately released and two of her close allies were named interim interior minister and speaker of the parliament.

Analysts say Tymoshenko remains a political force to be reckoned with, though she may now have been surpassed by opposition leaders such as former heavyweight boxing champion Vitali Klitschko and ally Arseniy Yatsenyuk, who spearheaded the Independence Square protests.

Tymoshenko was born in the industrial city of Dnipropetrovsk in central Ukraine and in her early career was aligned with power brokers from that region rather than the Donetsk stronghold of Yanukovych.

After rising to prominence as head of a gas utility, she became a deputy prime minister under the presidency of Leonid Kuchma in 1999, but was fired in 2001 after falling out with him. She was briefly imprisoned then on gas smuggling charges that were later quashed.

Her husband Olexander has now taken asylum in the Czech Republic. But their British-educated daughter Yevgenia, who married and then separated from a British heavy rock singer, has become one of the greatest defenders of her mother, with whom she bears a striking resemblance.