Greece officially began its second election campaign period this year, after opposition parties, as expected, conceded they can’t assemble a ruling majority in parliament to replace the outgoing government of Alexis Tsipras and his SYRIZA party.

The leader of newly-formed Popular Unity party Panagiotis Lafazanis returned his mandate to form a government – more formality than political opportunity – to Greece’s President Prokopis Pavlopoulos.

Vassiliki Thanou, president of Greece’s supreme court, was sworn in on Thursday as head of a caretaker government that will lead the heavily indebted nation until the elections expected next month.

President Pavlopoulos appointed Ms Thanou, 65, as the country’s first female prime minister, after leaders of the three main political parties failed to form a coalition to replace the government of outgoing Prime Minister Alexis Tsipras.

Her administration was expected to be sworn in yesterday (Friday).

Mr Tsipras announced his resignation last week and said he would seek a new mandate after members of his radical-left party, SYRIZA, rebelled over austerity measures demanded by the nation’s creditors.

The party won election in January on promises to end the deep budget cuts and tax increases imposed in exchange for two bailouts from Greece’s European partners and the International Monetary Fund, totalling nearly €245 billion ($380 billion) since 2010. Greece’s economy has contracted 25 per cent and unemployment soared to as high as 26 per cent over the five years of belt-tightening.

More than 60 per cent of Greek voters rejected the terms of a new package of loans in a referendum last month, only to have Mr Tsipras agree to even tougher conditions for a €85 billion bailout.

He said it was the best deal he could get to save Greece’s banks from imminent collapse, keep the country in the euro currency and avoid defaulting on international loans.

Parliament approved the agreement, but only with the support of opposition parties. The former energy minister, Panagiotis Lafazanis, broke with Syriza last week to form the new Popular Unity party.

Mr Tsipras said it was now up to voters to decide “who will lead Greece, and how”. He remains popular, but it is unclear whether Syriza can win enough parliamentary seats to govern without a coalition partner.

Tsipras rules out forming unity government.

In an interview Wednesday with Greece’s Alpha TV, Mr Tsipras ruled out forming a government with the conservative New Democracy, the socialist PASOK or the centrist To Potami parties.

That could leave Syriza’s current partner, the small, right-wing Independent Greeks, as the only viable option.

Mr Tsipras said even if he achieves a slim majority of 151 MPs in the country’s 300-seat parliament, he will still look for coalition with other parties, but he won’t remain Prime Minister if he has to cooperate with Greece’s old, systemic political parties.

The Greek premier faces the growing challenge of warding off a disintegration of his Syriza party, as many lawmakers and party members haven’t decided whether they will run in the forthcoming elections.

Last week, 25 of Syriza’s 149 members of parliament formed Popular Unity party, completing a divorce that has been looming since July, when Mr Tsipras agreed to the austerity-heavy terms of Greece’s European creditors, despite his party’s long-standing campaign to put an end to the harsh measures.

“It is a sad outcome, but not an unexpected one,” Mr Tsipras told local Alpha TV on Wednesday.

“What makes me sad is the attempt by the inner enemy to become the main enemy,” he said, adding that he was hurt that many of his ex-Syriza colleagues, who a few weeks ago feared a banking collapse, are now criticizing him.

Apart from Syriza’s hard-liners, members of another fraction within Syriza, the Group of 53, were this week considering whether to stand aside in the electoral battle.

The Group of 53, formed in mid-2014, stands ideologically between the hard-line Left Platform and Mr Tsipras’s relatively pragmatic group of core backers. Many of its members have been close aides to the party leader, but some abstained during the mid-August vote on Greece’s third bailout deal with the country’s creditors. Even if the group decides to stick with Syriza, it is expected to act as an opposition faction within the party.