It has gone quiet around the targeted takeover of Swiss agrochemicals giant Syngenta - Europe's largest player in terms of overall sales - by GMO titan Monsanto. Behind the scenes, however, the largest US and dominant global player is said to be working feverishly to push its plan forward.

An initial offer of 449 Swiss francs per share, representing an enterprise value of around $45 billion at current exchange rates, was rejected earlier by the Swiss player's board, which said it "fundamentally undervalued" the business and underestimated the "serious execution risks."

In exchange for a green light from Switzerland and a thumbs up from international regulatory authorities, Monsanto is now seen as prepared to put considerable additional cash on the table while at the same time agreeing to sell Syngenta's seeds and traits portfolio worth more than $3 billion in 2014 sales.

In a presentation to investors in New York, Monsanto President Brett Begemann said his group is "confident it can address all regulatory concerns." Without any divestments, a merger with Syngenta would create a market-dominating new global player with annual sales of $30 billion.

"We intend to make this a really clean deal, really easy to get done," Begemann said in New York. If Syngenta continues to reject an offer, he said Monsanto is "not precluded from developing relationships with other chemical suppliers."

Analysts suggested that the US group might strike a deal with conventional chemical crop protection producers such as BASF and Bayer to make a joint bid for Syngenta and subsequently strip the assets.

The Swiss group is the world's largest producer of conventional crop protection products and ranks third in seeds. Monsanto's sales are split by a ratio of around 70:30 between seeds and chemical crop protectants, while Syngenta's were nearly the reverse, with chemical products representing 75% and seeds 21%.

Monsanto is seen as needing to diversify to quell mounting criticism of its dominance in the GMO seeds industry, both from regulatory authorities and consumer advocates.