Monsanto Co
A CNBC report earlier in the day, citing an unnamed source, said that at least one major investor, hedge fund manager John Paulson, believes the two agricultural firms "continue to be in deal talks and aren't far apart on price."
US-traded Syngenta shares rose 3.7% in after-hours trading after the CNBC report.
Monsanto told Reuters that no deal talks are taking place, but said it has continued to hold out an invitation to Syngenta.
"We welcome and encourage Syngenta to engage in a direct, private dialogue with Monsanto, which has not happened to date," said Sara Miller, a spokeswoman for Monsanto.
Executives and other representatives from the two companies did meet earlier in the year to discuss Monsanto's unsolicited $45 billion offer.
Representatives from Syngenta declined to comment Tuesday. Paulson did not respond to a request for comment.

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