Tsipras sworn in as new Greek PM
Radical left leader Alexis Tsipras has been sworn in as Greece's new prime minister, becoming the youngest man to hold the post in 150 years.
The 40-year-old broke with tradition and took a secular oath rather than the Greek Orthodox religious ceremony with which prime ministers are usually sworn in.
Mr Tsipras' anti-bailout Syriza party gained the backing needed to form a government earlier by creating a surprise alliance with a small right-wing nationalist party.
Syriza won 36.3% of the vote in Sunday's early general elections, but fell two seats short of the necessary majority in the 300-seat parliament to form a government on its own.
The details of who will serve in the government and whether the two parties will form a coalition or whether there will be a Syriza-only minority government are expected to be announced later.
Mr Tsipras has promised to renegotiate Greece's massive bailout agreements, but has vowed not to take any unilateral action against lenders from other eurozone countries.
Mr Tsipras' choice to negotiate with the nationalist Independent Greeks - a party aligned in Europe with the UK Independence Party - rather than the centrist Potami caused concern that he could take a tough line in negotiations with rescue lenders.
Potami leader Stavros Theodorakis described the Independent Greeks as "far right and anti-European".
Syriza's financial planning official, Giorgos Stathakis, confirmed that the new government had no plans to meet with negotiators from the "troika" of the European Central Bank, the European Commission and the International Monetary Fund and would instead seek talks directly with governments.
Greek voters swung to the once-marginal left-wing party after five years of punishing austerity measures demanded under 240 billion euro (£179bn) bailout deals threw hundreds of thousands of people out of work and left nearly a third of the country without state health insurance.
Thousands of supporters turned out to watch Mr Tsipras speak in central Athens after his opponents conceded.
"The Greek people have written history," he said, to cheers.
"Greece is leaving behind catastrophic austerity, fear and autocratic government."
Outside the party's campaign tent in central Athens, supporters hugged each other and danced in celebration.
"It's like we've been born again and finally feel some hope," said Litsa Zarkada, a fired government cleaning worker.
"We were thrown into the street just before we could take our pension. We have been through so much."
The new government faces an immediate cash shortage, with a dwindling primary surplus, upcoming loan repayments, and limits on the money it can raise using treasury bill auctions.