Switzerland's Syngenta rejected a second takeover proposal from agrochemicals firm Monsanto on Monday, saying its U.S. rival had made no attempt to seriously address regulatory concerns over the potential deal.

Monsanto offered to pay a $2-billion reverse break-up fee to Syngenta if it cannot obtain global regulatory approvals for an acquisition, the firm said on Sunday. 

Syngenta issued a statement this morning saying "On June 6, Syngenta received a second letter from Monsanto which essentially repeated their first proposal of April 18. The only change by Monsanto is to add a wholly inadequate reverse regulatory break fee.  Monsanto's second letter represents the same inadequate price, same inadequate regulatory undertakings to close, same regulatory risks and same issues associated with dual headquarters' moves. As such, we have reiterated our prior rejection of Monsanto's proposal."

The Board of Syngenta confirmed that it has received an unsolicited proposal from Monsanto to acquire the company at a price of CHF449 per Syngenta share with approximately 45 percent in cash. Syngenta’s Board of Directors, in conjunction with its legal and financial advisers, has undertaken a thorough review of all aspects of Monsanto’s offer and has unanimously determined to reject Monsanto’s proposal as it is not in the best interests of Syngenta, its shareholders and its stakeholders. The offer fundamentally undervalues Syngenta’s prospects and underestimates the significant execution risks, including regulatory and public scrutiny at multiple levels in many countries.