AIX-EN-PROVENCE, France (Reuters) - Britain's vote to leave the European Union, or Brexit, questions the EU project's irreversibility and will have a negative impact on growth although its extent is still unclear, European Central Bank Executive Council member Benoit Coeure said on Sunday.

"Brexit created a climate of uncertainty, financial uncertainty in the short-term, and the Central Bank can answer that, it already did," Coeure told a business conference in the southern French city of Aix-en-Provence.

"We have instruments that we are ready to use, thank God we didn't have to use them so far, but we are ready to do so."

Coeure said last week it was urgent to clarify the calendar for Britain's exit from the EU because prolonged uncertainty would have an economic cost, first of all for Britain but also for the EU.

(Reporting by Michel Rose, editing by Sybille de La Hamaide)