ROME — Italian Premier Enrico Letta announced Thursday that he is resigning after a party rival withdrew essential support for the tattered, 10-month-old coalition government with the aim of getting the premiership for himself.

Letta said he will hand in his resignation to Italy's president on Friday. He cited the overwhelming vote against him by his Democratic Party leadership.

Hours earlier, the party leader, Florence Mayor Matteo Renzi — who has been maneuvering for months to become premier — said it was time for "radical change" in economically stagnant and politically unstable Italy.

President Giorgio Napolitano, who has staunchly opposed calling for new elections, could conceivably ask Letta to try to win a vote of renewed confidence in Parliament to make the legislature, and not the Democratic Party, the arbiter of the premier's fate. But after the Democrats, the government's main partner in the shaky coalition, lost faith in Letta, his chances of commanding a majority in Parliament appeared bleak.

Napolitano would then likely ask Renzi to form a coalition solid enough to command a working majority in Parliament that could quickly enact electoral, economic and other needed legislation.

Renzi has depicted himself as a fresh face in Italian politics, positioning himself to be the dominant politician in Italy after Silvio Berlusconi, the former premier who was banned from holding public office after a tax fraud conviction.

Whether Renzi's power grab might alienate potential voters is a big unknown. Renzi said he realizes there is a "risk he could be burned."

Italian voters might be irked that they aren't picking their government's leader at the ballot box. Letta didn't run for office, but was asked by Napolitano to try to end weeks of political stalemate.

The last candidate for premier to be elected in Italy was Berlusconi in 2008. But the 2011 financial market crisis forced the media mogul to resign, and Napolitano then tapped economist Mario Monti to lead a non-elected government of technocrats.

Letta became premier in April, two months after inconclusive elections.