Italian President Giorgio Napolitano signs his resignation at the Quirinale presidential palace in Rome January 14, 2015. [Photo/Agencies]

ROME - Ageing Italian President Giorgio Napolitano resigned on Wednesday before the natural end of his second seven-year tenure, amid growing ferment in politics for the choice of his successor.

Senate speaker Pietro Grasso, the second executive of state, took the temporary presidency and will hold the presidential powers until a new head of state is appointed.

A statement issued by the Chamber of Deputies, or lower chamber, said parliament, composed of 630 deputies, 315 senators and currently six senators for life including Napolitano who serves as senator for life like all former presidents, will meet along with 58 regional representatives on Jan 29 to start presidential elections, within 15 days from the president's resignation as established by the Italian Constitution.

The election will take place by secret ballot with a majority vote cast by two-thirds of the assembly in the first three rounds of balloting, after which a simple majority is sufficient.

In this lapse of time, labored negotiations for the choice of a new president, who can be any Italian citizen aged at least 50 and in possession of all civil and political rights, are expected to take place among political parties.

A number of potential candidates have been mentioned by the local press in recent weeks including former Rome mayor Walter Veltroni, constitutional court judge Sergio Mattarella, former prime ministers Giuliano Amato and Romano Prodi, Foreign Minister Paolo Gentiloni, Defence Minister Roberta Pinotti and former national anti-mafia prosecutor Grasso himself.