NEW YORK - Mayor Michael Bloomberg took the stunning step Tuesday of announcing that he has left the Republican Party and switched to unaffiliated, a move certain to heighten presidential speculation despite his repeated denials that he is running.

The billionaire former CEO, who was a lifelong Democrat before he switched to the Republican Party for his first mayoral run in 2001, said the change in his voter registration does not mean he is running for president.

“Although my plans for the future haven't changed, I believe this brings my affiliation into alignment with how I have led and will continue to lead our city,” Bloomberg said in a statement.

The 65-year-old mayor has increasingly been the subject of speculation that he will run as an independent in 2008, despite his repeated promises to leave politics after the end of his term in 2009.