Alexis Tsipras has been sworn in as Greece's prime minister after his antiausterity Syriza party won January 25 parliamentary polls.
Earlier on January 26, Tsipras's leftist party struck a deal with a right-wing populist party, the Independent Greeks, to form a government after Syriza fell just short of the majority needed to govern alone.
The new government is expected to be unveiled on January 27.
With 99.9 of the ballots counted, Syriza won 36 percent of the vote, giving it 149 seats in the 300-seat parliament. The Independent Greeks won around 4 percent and 13 seats.
The two parties agree on little except their mutual hostility toward the terms under which Greece received an international bailout that saved it from bankruptcy in 2010.
It is the first time a member of the 19-nation eurozone will be led by a party rejecting EU-imposed austerity measures.
Greece has received $270 billion in international bailouts since 2010 to avoid bankruptcy.
Syriza campaigned hard on renegotiating the EU-International Monetary Fund bailout that imposed strict spending and taxation rules on Athens.
Tsipras has promised not to take any unilateral action against lenders from other eurozone countries.
The possibility of Greece defaulting on its debt repayments is likely to spark renewed fears the country could be forced to leave the eurozone.
Eurogroup chief Jeroen Dijsselbloem warned Greece on January 26 that the country's eurozone membership depended on Athens sticking to prior agreements.
"Membership of the eurozone means that you comply with everything you have agreed with," Dijsselbloem said. "On that basis, we're ready to work with them."
Germany and Britain also said they expected the new Greek government to uphold its commitments to international creditors.
"In our view it is important for the new government to take action to foster Greece's continued economic recovery," said a spokeswoman for German Chancellor Angela Merkel. "That also means Greece sticking to its previous commitments."
In London, the office of the Prime Minister David Cameron said: "Greece needs to deal with its deficit and meet its international commitments."
Finnish Prime Minister Alexander Stubb warned on January 26 that his country "will not accept a demand for debt cancellation," but was willing to discuss further extensions to Greece's bailout.
With reporting by AP, AFP, Reuters, and dpa