Monsanto's board is set to meet today to decide whether to approve a sale to Germany's Bayer for more than $65 billion after concluding more than four months of negotiations, people familiar with the matter said.

The deal is expected to value Monsanto, the world's largest seeds firm, at a little more than the sweetened $127.50 per share cash offer that the German pharmaceuticals and crop chemicals maker disclosed last week, the people told Reuters.

Bayer's supervisory board is due to follow suit and meet on Wednesday to deliberate on Monsanto's response, the sources said, adding that it is still possible that the deal hits a snag with the board of either company.

The sources asked not to be identified because the deliberations are confidential. Bayer and Monsanto declined to comment.

Monsanto's shares were 1 per cent lower at $105.82 at 1513 GMT, when Bayer's shares were down 0.3 per cent at €93.29.

Bayer said last week talks with Monsanto had advanced and that it was willing to offer $127.50 per share for the world's largest seeds company, up from $125 previously, valuing the company at more than $65 billion, including debt.

Sources told Reuters that topping up the price secured Bayer access to more privileged information on Monsanto's business performance and paved the way for more detailed negotiations.

"Given recent updates on the Monsanto approach suggest a final conclusion may be close, we suspect (Bayer) will work hard to try and reach a final conclusion before the Meet Management event, if possible," Jefferies Research analyst Jeffrey Wolford said in a research note before the news, referring to Bayer's presentations day for analysts and investors in Cologne next Tuesday.

Bayer is trying to combine its crop chemicals business, the world's second-largest after Syngenta, with Monsanto's industry-leading seeds business, the latest in a series of major consolidation moves in the agrochemical sector.

US chemicals giants Dow Chemical and DuPont have agreed to merge and spin off their respective seeds and crop chemicals operations into a major agribusiness.

Syngenta last year fought off unwanted suitor Monsanto, only to later agree to a takeover by ChemChina.

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