Germany looks set to abstain in a European Union vote next week on the continued use of glyphosate in weed killers because ministries run by different parties remain at odds over the chemical which some experts say could be carcinogenic.

Glyphosate is used in many herbicides including Monsanto's Roundup, despite a dispute between EU and U.N. agencies over whether it causes cancer.

Experts from the EU's 28 member states will hold a closed-door meeting on Wednesday and Thursday in Brussels to discuss a draft proposal, seen by Reuters, to extend by nine years approval of the herbicide.

Last month, European politicians advised that glyphosate should only be approved for another seven years, rather than the 15 proposed by the EU executive, and should not be used by the general public.

The European Commission said the new draft takes into account the opposition and maintains the proposal to ban some products because of the substances they combine with glyphosate, which could add to risks.

It said the banned "list of co-formulants" includes POE-tallowamine from glyphosate-containing pesticides.

"The common agreement remains that the attention must be focused on co-formulants," a spokeswoman for the Commission said. "If need be, they will lead to a review of the approval of the active substance." An EU source, speaking on condition of anonymity, said at least one big member state maintained opposition to renewal, which the EU executive says is needed to prevent a legal vacuum when the existing authorization lapses at the end of June.

But Germany's conservatives (CDU) and their junior coalition partner, the Social Democrats (SPD) cannot agree on a common position. If the German government cannot reach agreement, it will abstain from voting.

"It's proven that glyphosate has negative effects on the environment. That needs to be fully taken into account for the approval," Environment Minister Barbara Hendricks, an SPD member, told Reuters.

"Given that there is still uncertainty about the health risks associated with glyphosate, the SPD-led ministries will not agree to the approval of glyphosate," she said. Agriculture Minister Christian Schmidt, a member of the Christian Social Union (CSU) - sister party to Chancellor Angela Merkel's Christian Democrats (CDU) - has, up until now, signaled that he would agree to the weed killer being approved. Martin Haeusling, a German lawmaker for the Greens in the European Parliament, said a qualified majority for the approval was not certain if Germany abstained from voting. Environmental campaigners have demanded a full ban on glyphosate.

"It is scandalous that the Commission is ramming through an EU approval for glyphosate to be used with no restrictions, despite the very serious concerns about the impact of this toxic substance on public health and the environment," said Green member of European Parliament and food safety spokesperson Bart Staes.

"Clearly banning glyphosate would be the responsible course of action," he said.

(Reporting by Alissa de Carbonnel in Brussels and Hans-Edzard Busemann in Berlin; Writing by Michelle Martin and Alissa de Carbonnel; Editing by Dominic Evans)