A former prime minister whose party won Bulgaria's May 12 election says his party doesn't have enough seats in parliament to form a stable government.

Boiko Borisov made that decision Thursday, saying his center-right GERB party only has 97 of parliament's 240 seats, and that isn't enough to succeed.

That means President Rosen Plevneliev is now expected to ask the Socialists, who finished second in the election with 84 seats, to take on that role.

The Socialists have said they will try to form a Cabinet of technocrats with wide support, led by a former nonpartisan finance minister, Plamen Oresharski.

Borisov resigned as prime minister in February amid sometimes violent protests against widespread poverty and corruption in Bulgaria.