U.S. biotechnology firm Genzyme and its French suitor Sanofi-Aventis are at odds over the threshold price at which Sanofi could begin the due diligence on Genzyme's books, the Wall Street Journal said, citing people familiar with the matter.

Both Genzyme and Sanofi are yet to agree on the threshold price and that is the main reason why the talks have not progressed further, the people told the Journal.

Genzyme may open its books to Sanofi if the French company agrees to offer around $75 a share as a starting point for negotiations on a possible sale, the paper said.

However, Genzyme may not sell unless a bid of at least $80 a share is made, people familiar with the matter told the paper. A representative for Sanofi declined comment to the Journal. The newspaper said Genzyme did not respond to a request for comment.

After an initial flurry of leaks to the media, in which the French drugmaker was reported to have offered $69 a share to acquire Genzyme, both sides  have gone silent.