Bayer, which bought Roundup maker Monsanto last year, has reportedly offered $8 billion to settle thousands cancer claims.

Lawyers for the consumers who claim glyphosate, the active ingredient in Roundup, caused their cancer, want $10 billion, according to Bloomberg.

However, mediator Ken Feinberg told Reuters that the reported offer is "pure fiction."

Bayer's stock price has fallen by half since its June 6, 2018, purchase of Monsanto.

Monsanto parent company Bayer is said to be offering an $8 billion deal to settle about 18,000 claims that its weedkiller Roundup causes cancer. Shares of Bayer jumped ahead of the start of trade Friday on optimism that a settlement would end uncertainty about the chemical giant's liabilities.

The offer is less than the $10 billion requested by lawyers representing consumers who claim their cancers were caused by glyphosate, the active ingredient in Roundup, according to Bloomberg News, which cited people familiar with the negotiations. It could take months to reach a deal, and there's no assurance the sides will come to an agreement, the publication added.

However, a report in Reuters refuted the settlement offer, with mediator Ken Feinberg saying Bayer has not offered to pay billions of dollars to settle the claims.

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"Bayer has not proposed paying $8 billion to settle all the U.S. Roundup cancer claims. Such a statement is pure fiction," Feinberg told Reuters Friday. "Compensation has not even been discussed in the global mediation discussions."

Bayer didn't return a request for comment. Still, the prospect of a settlement cheered investors, sending Bayer shares up 4.7% on Friday.

"$8 billion would be lower than most analysts are forecasting and many investors fearing," Markus Mayer, an analyst at Baader Helvea, told Bloomberg.

Glyphosate is facing an unprecedented tests both in the courtroom and in America's homes amid rising concern about the safety of the chemical. Tests from environmental groups are adding to consumer worries, such as a recent study finding that 21 oat-based cereal and snack products, including Cheerios, contain traces of glyphosate.

Since Bayer bought Roundup's maker Monsanto last year, the German chemical giant has lost three high-profile court cases over the chemical's possible link to cancer.

Investors have fled Bayer over concerns about its potential liabilities, halving the company's stock price since its June 6, 2018, purchase of Monsanto. In its most recent annual report, Bayer said it expects more lawsuits to emerge.