France has contacted Swiss authorities for help in determining whether 353 prospective UBS clients in France have undeclared assets in Switzerland...as part of an ongoing French probe into UBS's business practices and whether the bank offered illicit products that would avoid tax...Le Monde said the French Budget Ministry confirmed the existence of the probe and said 850 million euros ($1.1 billion) were at stake...UBS France's head, Jean-Frederic de Leusse, told the newspaper the bank was cooperating fully with the authorities...UBS is still being probed by the French judiciary over whether it offered potential French clients investments that were allegedly designed to cheat the taxman. Three UBS France executives are being investigated as part of the probe, a judicial source told Reuters.