Sanofi Aventis Chief Executive Chris Viehbacher said in an interview that the French pharmaceuticals group's offer for Genzyme could be extended for a third time, beyond the Feb. 15 deadline.

Asked by La Tribune newspaper about the deadline, Viehbacher said: "It is a possibility, there are no limits on takeover offers in the United States."

He added: "It is normal to spend time on an operation of $18.5 billion."

Viehbacher's interview is to be published in La Tribune business newspaper on Thursday and was made available late on Wednesday.