France's health and safety agency is poised to ban weedkillers that combine chemicals glyphosate and tallowamine because of concerns over possible health risks, it said Friday.

The ANSES agency sent a letter this week to manufacturers informing them that it intends to withdraw the authorization for such products, Francoise Weber, the ANSES deputy director-general, told Reuters.

The agency had reviewed products combining glyphosate and tallowamine after conclusions published in November by the European Food Safety Agency suggested there were greater potential health risks in combined use rather than when glyphosate is used alone, she said.

"It is not possible to guarantee that compositions containing glyphosate and tallowamine do not entail negative effects on human health," Weber said.

Glyphosate, the active ingredient in Monsanto's Roundup weedkiller, has stirred fierce debate over the past year since a World Health Organisation body classified it as a probable carcinogenic, and EU countries are discussing whether or not to extend its EU-wide license.

France's environment minister has been pushing for an EU-wide ban on glyphosate-based products and is also supporting legislation that would outlaw a type of pesticide blamed for harming bees.

Tallowamine is used in weedkillers to allow them to be absorbed effectively by plants.

It is combined with glyphosate in many weedkillers but a large number of glyphosate products without tallowamine are available in France, Weber said.

Glyphosate and tallowamine combinations were previously withdrawn voluntarily from the German market by manufacturers, she added.

Monsanto said the commercial impact would be "minimal" as it had already shifted away from using tallowamine.

"The elimination of glyphosate sales in France by itself should not have a material effect on Monsanto, maybe $20 million of earnings impact. If it spreads to the rest of Europe the impact would be greater though, as Europe is a premium market; could lead to up to $100 million of earnings impact," Bernstein analyst Jonas Oxgaard said in an email to Reuters.

In an emailed statement, Monsanto described the glyphosate debate in Europe as "political" and said that tallowamine-based products "do not pose an imminent risk for human health when used according to instructions."

Arguments over glyphosate have divided scientists and pitched environmental protection groups against chemical companies and farmers who say there are no viable alternatives.

A final decision by ANSES on withdrawing glyphosate-tallowamine mixtures would take at least several weeks because the agency must first consider comments by the manufacturers, who have two weeks to submit arguments, Weber said.