Rumors French pharmaceutical giant Sanofi-Aventis SA is chasing a big U.S. acquisition have driven up shares of companies investors think might be a target.

Shares of Allergan Inc. jumped as much as 9 percent, while Genzyme Corp. and Biogen Idec Inc. both were up at least 5 percent.

That's after a report by Bloomberg indicated that Sanofi Chief Executive Chris Viehbacher this week briefed his board at a special meeting, saying that the company is working on a deal for a major acquisition in the U.S.

The report says the deal is in the very early stages and does not identify the American company.

A Sanofi spokesman in the U.S. says the company does not comment on market rumors.