Predators are stalking not only Swiss specialty chemicals producer Clariant, but also agrochemicals giant Syngenta.

Following a report by news agency Bloomberg that US rival Monsanto had again made takeover overtures to Syngenta, stock market speculation propelled the Swiss company's shares on the Zurich stock exchange.

The news agency said Monsanto and Syngenta had held preliminary talks last year about a $40 billion takeover by Monsanto to create the world's largest agrochemical producer.

Both companies have declined to comment on the rumors.

Analysts believe the two would be a good match, but due to considerable overlap, in particular in markets for maize and soy seeds, observers note that convincing antitrust authorities of the deal would be a tough task.

US authorities would have the greatest concerns, reports say.

Syngenta is the world's largest producer of conventional pesticides, herbicides and fungicides, while Monsanto is the market leader in genetically manipulated maize. A merger of the two groups would create a new market player with annual sales of more than $30 billion.