He said "an investigating judge came to the Paris headquarters of UBS France in connection with his probe," confirming information given by a source
close to the affair.
Two people have been charged with money laundering and complicity in illegal soliciting of business following an investigation opened last year into UBS's business practices.
Police have also raided the bank's offices in Strasbourg, Lyon and Bordeaux, detaining several employees.
UBS is suspected of having helped clients hide transfers of funds between France and Switzerland and of allowing its Swiss operations to illegally canvass for clients in France.
UBS paid a fine of €544.6 million ($708 million, 658.5 million francs) to the United States in 2009 to settle a tax fraud case which charged that it helped US citizens open offshore accounts to avoid paying taxes.
Authorities in several European countries are probing suspected tax evasion involving Swiss banks, including in France and in Germany, where fiscal authorities earlier this month raided several clients of bank Credit Suisse living in the country.