French drugmaker Sanofi-Aventis, faced with looming generic competition for its top-selling product, said on Friday it was cutting its U.S. pharmaceutical operations by about 25%, which amounts to the loss of some 1,700 jobs.

The majority of the job cuts - about 1,400 - will come from Sanofi's U.S. sales force, company spokesman Jack Cox said.

Sanofi, which is trying to buy U.S. biotechnology company Genzyme for more than $18 billion, said it will streamline its U.S. pharmaceutical operation to focus on three therapeutic areas - diabetes, atrial fibrillation and oncology.

As early as late next year, the company is facing the U.S. patent expiration of the blood clot preventer Plavix that it markets with Bristol-Myers Squibb. Plavix is the world's second largest selling medicine with annual worldwide sales of about $9 billion.

Sanofi currently has 13,000 employees based in the U.S. with 6,900 in its pharmaceutical operations division.