Still no official word but unnamed sources are claiming that Sanofi-Aventis has now made a takeover bid for Genzyme Corp worth around $18.40 billion.

Reuters is citing “sources familiar with the situation” that the Paris-headquartered firm has made an offer valued at about $69 per share, and the two sides are discussing the offer. The sources claim that Sanofi's board have authorised a bid up to $70 per share, which would value Genzyme at $18.7 billion.

However, the news agency adds that while the two firms are communicating, they remain far apart on price and Genzyme are unlikely to accept a deal under $80 per share, or $21.4 billion. The US biotech is trading around the $70 mark at the moment.

Most observers are predicting that Sanofi would have to lift any bid to around $75-$80 per share. Genzyme, which has suffered manufacturing problems since last year, is thought to be looking at a bid of around $20 billion reflecting the potential for a turnaround.

If Genzyme is indeed talking, this could bring out other possible suitors and GlaxoSmithKline, Johnson & Johnson, Pfizer and Amgen have been mentioned as potential purchasers.

In an investor’s note, Citigroup analysts Mark Dainty and Yaron Werber said that “the process for an acquisition of Genzyme by Sanofi appears to be accelerating." They added that given Sanofi is likely the only buyer “and that shareholders are aware that Genzyme could likely trade down to low/mid $50s in case a deal is not reached, we see the deal getting done at $74-77”.

It is also thought that billionaire investor Carl Icahn, who has a 4.9% stake of Genzyme, would like to see a deal done at around the mid-$70 range, having bought in at $54, the Citi analysts added.