Tsipras took a civil oath on Monday, pledging to "uphold the constitution and laws" of the southern European country, struggling with a protracted debt crisis.

Syriza received 35.5 percent of the votes in the snap elections, whereas the conservative New Democracy party got 28. Only 57 percent of the electorate cast votes - the lowest turnout in recent Greek history.

To achieve the absolute majority necessary to govern - having fallen six seats short at 145 spots - Tsipras plans to form a coalition government with the small right-wing Independent Greeks party, which polled less than 4 percent of the vote.

Tsipras is expected to name his cabinet ministers on Wednesday.

Merkel's phone call to Tsipras

German Chancellor Angela Merkel telephoned the Greek leader on Monday to congratulate him on his victory.

"The Chancellor and Alexis Tsipras exchanged views on the forthcoming special meeting of the European Council on Wednesday and on the bilateral issues to be discussed … and agreed on cooperating closely on the European policy issues," read a statement released by the German government.

Earlier on Monday, the European Union also congratulated Tsipras on winning the elections, but said Greece should waste no time in implementing economic reforms attached to its international bailout.

"The Commission congratulates Alexis Tsipras for his victory," European Commission spokesman Margaritis Schinas told reporters in Brussels. "The new government will now have the mandate to carry out those reforms ... There is a lot of work ahead and no time to lose."

Tsipras on migrants

The Greek leader criticized the European Union's handling of the ongoing refugee crisis after taking his oath of office and urged all member states to share the responsibility.

"Greece is a first reception country, and Europe has unfortunately not taken steps to protect reception countries from a [migration] wave which has taken on uncontrolled dimensions," he said. "There is a need ...that Europe deal with a global, a European problem and share the responsibility among all member states."

Thousands of people are fleeing a civil war in Syria and heading to Europe via the Mediterranean. The arrival of these refugees has sparked major upheaval in Europe, with many governments imposing strict border checks to impede and manage the overflow of migrants.

EU leaders were due to discuss the crisis at an extraordinary summit on Wednesday.

shs/msh (dpa, AFP, Reuters)