Monsanto said it still believed in the value of a combination of the two agricultural seed and chemical giants, but will focus on building its core business and meeting long-term growth objectives.
Monsanto confirmed that it made a revised offer to Syngenta on Aug. 18, raising a previous offer to 470 Swiss francs, a value of roughly $47 billion. It also confirmed it raised a reverse break-up fee offer to $3 billion.
But, Monsanto said in a statement, Syngenta continued to spurn the overtures.
"Without a basis for constructive engagement from Syngenta, Monsanto will continue to focus on its growth opportunities built on its existing core business..." the company said in a statement.
Syngenta shares in Switzerland closed more than 18 percent lower on the news that the deal was off the cards.
U.S.-listed Monsanto shares traded nearly 8 percent higher.
There was no immediate comment from Syngenta.
Monsanto has said that it wanted to acquire Syngenta primarily to boost its agrichemicals portfolio, which now relies mainly on glyphosate-based herbicides branded as Roundup.
Monsanto is the world's largest seed company and known for its development of genetically altered corn, soybeans, canola and other crops, while Syngenta is the world's largest agrichemical company.
In July, Syngenta CEO Mike Mack told CNBC that the offer then on the table was "completely inadequate."
Check out the interview below to hear more: