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(Reuters) - Bayer AG’s plan to win antitrust approval to buy U.S. seeds supplier Monsanto Co has not satisfied U.S. officials, who are worried the $62.5 billion merger could hurt competition, Bloomberg reported on Thursday.

Shares of Monsanto fell 4 percent in heavy afternoon trading following the news.

The U.S. Department of Justice wants Bayer to divest more assets to satisfy its conditions, and does not think the German chemicals company’s current proposal is sufficient, Bloomberg reported, citing people familiar with the matter.

Monsanto spokeswoman Sara Miller declined to comment. A Bayer spokesman said the company would not comment on rumors, but added it remains in talks with regulators to help close the deal in the second quarter of the year.

Bayer had pledged to sell certain seed and herbicide assets for 5.9 billion euros ($7.26 billion) to BASF to address EU regulatory concerns and has separately offered to sell its vegetable seeds business to BASF. [nL5N1QP3ET]

The company has secured an approval from Brazilian regulators for the merger, while it is in the frame to win conditional antitrust approval from the European Union, Reuters reported this week. [nL3N1QV4EG]

Bayer also has conditional approval from China’s commerce ministry.

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