Greek leftist leader Tsipras claims victory

Outgoing Greek Prime Minister Antonis Samaras reacts before a news conference following an updated exit poll in Athens, January 25, 2015. [Photo/Agencies]

Tsipras said he would cooperate with fellow euro zone leaders for "a fair and mutually beneficial solution" but said the Greek people came first. "Our priority from the very first day will be to deal with the big wounds left by the crisis," he said. "Our foremost priority is that our country and our people regain their lost dignity."

He has promised to keep Greece in the euro and has toned down some of his rhetoric but his arrival in power would mark the biggest challenge yet to the approach adopted to the crisis by euro zone governments.

Syriza's victory is likely to encourage other anti-austerity parties which are winning support across Europe, such as the Podemos movement in Spain.

But it might also strengthen the hand of mainstream leaders including French President Francois Hollande and Italian Prime Minister Minister Matteo Renzi who argue that orthodox austerity policies have failed to produce the economic growth which Europe needs to recover fully from the global financial crisis.

Hollande expressed in a statement his "desire to pursue the close cooperation between our two countries in service of growth and the stability of the euro zone".

Finnish Foreign Minister Erkki Tuomioja was more forthright, saying he believed the result would change the debate in Europe and put more emphasis on growth and employment. "This is a slap at what I see as a very right-wing economic policy in Europe," Tuomioja, a Social Democrat, told the website of the Helsingin Sanomat newspaper.

However with Greece's economy unlikely to recover for years, Tsipras faces enormous problems and his victory raises the prospect of tough negotiations with European partners including German Chancellor Angela Merkel.

Greece's bailout deal with the euro zone is due to end on Feb. 28 and Tsipras' immediate challenge will be to settle doubts over the next installment of more than 7 billion euros in international aid. EU finance ministers are due to discuss the issue in Brussels on Monday.

If Syriza falls short of a majority, Tsipras will have to try to build a coalition with smaller parties or form a minority government with ad-hoc support from others in parliament.

"It's a historic win," said Athens-based political analyst John Loulis, adding that Tsipras would have to form a coalition to prevent renewed instability. "He has no other option, the last thing the country needs would be another round of elections

Negotiations are likely to begin immediately, and both the small Independent Greeks party and centrist To Potami party, said they would be willing to support an anti-bailout government. If Syriza requires support to govern, it may find itself hostage to its partners' demands, raising questions over how durable a Tsipras government would prove.