Paris - France's Emmanuel Macron vowed after stepping down as economy minister on Tuesday to "transform" an ailing country, but stopped short of declaring a presidential run.
The 38-year-old said he had "seen at first hand the limits of our political system" and that quitting the government of President Francois Hollande would enable him "to be free" to push forward his own agenda.
With elections eight months away, the former investment banker said: "I am determined to do everything so that our values, our ideas, our actions can transform France as soon as next year".
While Macron's resignation clears the way for a presidential bid, it is unclear how wide the appeal really is of such a young man who has never held elected office.
An opinion survey last month nevertheless gave him a 41% approval rating.
On Tuesday Macron charged that France's political system is broken, and that his movement called "En Marche" (On the Move) would put forward a "diagnosis" of the country's woes next month.
"I will then propose far-reaching action that can be taken," he said.
Macron's departure is a blow to Hollande, whose approval ratings are the lowest of any post-war French president. He has pledged not to seek re-election if he fails to rein in stubbornly high unemployment, which is hovering at around 10%.
Hollande has said he will not decide on a re-election bid until the end of the year.
The embattled president, who has already alienated the left flank of the Socialist Party through economic and labour reforms, faces further isolation with the loss of the star of his government's centrist flank.
Macron would be a fresh face in a presidential field that includes former president Nicolas Sarkozy, 61, and 71-year-old ex-prime minister Alain Juppe - both right-wing candidates.
Juppe is France's most popular politician, but Sarkozy is closing the gap fast. A poll this week showed both would score 34% in November's centre-right primary.
Marine Le Pen, 48, of the far-right anti-immigration National Front, is standing for a second time in presidential elections and many polls show she is likely to reach the second round of voting.
Applauded by liberals for challenging the key planks of French socialism such as the 35-hour work week, the former Rothschild banker and self-made millionaire is criticised by die-hard leftists as being too cosy with big business.
His name is on the first of two economic reform packages that were forced through parliament without a vote under Hollande.
Both sparked angry street protests and created a deep divide within the Socialist Party.
But Macron's straight-talking, anti-establishment flair has seen him win over many young, cosmopolitan French people.
The two-round presidential election will be held on April 23 and May 7, 2017.