PARIS (Reuters) - France's health and safety agency has decided to ban weedkillers that combine chemicals glyphosate and tallowamine because of uncertainty over possible health risks, it said on 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 (EFSA) suggested greater potential risks compared with glyphosate 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 by telephone.

Glyphosate, a common ingredient in weedkillers such as Monsanto's Roundup, has been the subject of fierce debate in the past year since a World Health Organisation body classified it as probably carcinogenic, and European Union 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 going through the French parliament that would outlaw a type of pesticide blamed for harming honey bees.

Tallowamine, technically referred to as polyethoxylated (POE) tallowamine, is used in weedkillers to allow them to be absorbed effectively by plants.

The substance 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Glyphosate and tallowamine combinations were previously withdrawn from the German market in a voluntary step by manufacturers, she added.

Monsanto said the commercial impact on the company would be "minimal" given that it had already shifted away from using tallowamine.

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

Like the debate over pesticides and bees, arguments over glyphosate weedkillers 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, which have two weeks to submit arguments, Weber said.

(Reporting by Gus Trompiz; Editing by Bate Felix and David Goodman)