"#Brexit: 2,500 jobs already announced for Ile-de-France, with a target of 10,000 by 2019," Valerie Pecresse tweeted on a visit to London to meet representatives of 70 internationally-focused companies based in London.
Pecresse's figure concerns large financial companies, so the total could be closer to 3,500 and 4,000 posts once small businesses are taken into account, Arnaud de Bresson, chief executive of financial lobby group Paris Europlace and who was part of the visit, told AFP by telephone.
The Bank of England said this month that 10,000 UK financial services jobs could move abroad on the first day of Brexit, after warnings of up to 75,000 relocations in total.
Britain is set to leave the bloc in March 2019, but remains locked in tough exit negotiations with the EU.