Alexis Tsipras says outcome of the vote robs government of any 'political or moral legitimacy' to continue with austerity policies

The election marked a turning point for Greece on Sunday with voters delivering a resounding victory for the radical left Syriza party while sending at least three neo-nazi Golden Dawn members to Brussels.

In a historic day for the left, the anti-austerity Syriza won the ballot by a margin of nearly four points over the conservative New Democracy party led by prime minister Antonis Samaras. Addressing supporters as the results rolled in, Alexis Tsipras, Syriza's leader, called for general elections to be held immediately, saying the outcome robbed the government of any "political or moral legitimacy" to continue enforcing policies that were overwhelming rejected.

As the country on the frontline of Europe's debt crisis, Greece has been forced to adopt excruciating reforms and spending cuts in return for rescue packages sponsored by the EU and International Monetary Fund.

"Tomorrow all of Europe will be talking about Syriza," said the 39-year-oldTsipras, also the European Left's candidate for commission president. "Already the peoples of Europe are celebrating the defeat of the memorandum [the accord outlining Athens' two bailout agreements] in the country chosen as a guinea pig by the European leadership.".

But with nearly half of the vote counted and 26.4% compared with the two-party coalition's combined 30.2 %, Samaras insisted that the result had not been the endorsement Syriza had been looking for to overturn the government.

Instead, with about 9.37% of the vote it was the far-right Golden Dawn's showing that is likely to shake the Greek political establishment most.

Following up on their strong performance in local elections last week, the extremists were catapulted into third place in the country's political constellation, behind Syriza and New Democracy.

Although stridently anti-EU and anti-bailout – sentiments that speak increasingly to the heart and minds of a nation felled by the debt crisis – Golden Dawn is also the most vicious far-right party on the continent of Europe with a third of its leadership in prison on charges of running a criminal organisation.

In a first for any political force, the extremists who have recently gone out of their way to soften their image but are the focus of a government-ordered judicial investigation, have been accused of murder, racial violence, illegal weapons possession and extortion.

In a message delivered from his Athenian prison cell, Golden Dawn's leader Nikos Michaloliakos told supporters: "I congratulate you for managing to resist the government's terrorism and for not believing their lies. We are the only political power that actually stands up against our state being run by foreign powers …

"Golden Dawn is now the third force in the political life of the country. New Democracy paid the price for their policies against our people … and Syriza has failed to express the public anger. Our slogan was the thieves should be in prison and the money they embezzled returned to the people but the thieves managed to put us in jail," he railed. "They tried to dig a grave for us but they fell in it themselves."

In its bid to gain international acceptability, Golden Dawn has recently made overtures to other far-right parties in the EU. Its spokesman and candidate for Athens mayor, Ilias Kasidiaris, last week described France's Marine Le Pen as a "visionary." Le Pen's Front National has repeatedly rejected calls for cooperation from Golden Dawn whose symbol resembles the Swastika and whose leaders have publicly applauded Adolf Hitler.