ATHENS, Greece (AP) — Senior judge Ioannis Sarmas was sworn in Thursday as Greece's caretaker Prime Minister who will head the country until new national elections are held in about a month.

Sarmas, 66, took over from center-right Prime Minister Kyriakos Mitsotakis, who won a landslide victory in parliamentary elections on May 21 but was unable to form a government. Although his New Democracy party beat the leftwing main opposition Syriza by 20 points — the biggest margin in 50 years — the one-off electoral system left it five seats short of a majority in the 300-seat Parliament.

Syriza and the third-placed Pasok Socialists also proved unable to form a coalition. Therefore new elections will be held, with June 25 seen as the likeliest date, under a different electoral system which gives the first party up to 50 extra seats in Parliament. Mitsotakis hopes that vote will secure him a governing majority.

Sarmas will head a 16-member caretaker government, in which a former Greek ambassador to the U.S., Vassilios Kaskarelis, will be Foreign Minister. The key finance ministry will be headed by economist Theodore Pelagidis, deputy governor of Greece's central bank.