Italy's President Giorgio Napolitano has resigned as promised, less than two years after accepting an unprecedented second term as head of state because squabbling lawmakers couldn't agree on a successor.

The Quirinal presidential palace said Napolitano, who turns 90 this year, signed his formal resignation late Wednesday morning.

Napolitano reluctantly agreed in spring 2013 to stay on for a second term when lawmakers repeatedly failed to elect his successor. He made clear then because of age, he wouldn't serve the entire new term. In recent weeks he repeatedly indicated he would step down in mid-January.

Now Parliament and special regional electors must hold a special voting session in 15 days to pick a new president. The largely ceremonial office is usually held by someone considered above the political fray.