The European Commission is extending by 18 months its approval for weed-killer glyphosate, used in Monsanto's Roundup, Health Commissioner Vytenis Andriukaitis said.

Contradictory findings on carcinogenic risks have thrust the chemical into the center of a dispute between EU and U.S. politicians, regulators and researchers.

Campaign groups urged governments to exercise caution and EU member states repeatedly failed to take a decision to extend the license approval, which expires at the end of the month.

"The Commission will follow our legal obligation. We know very well that we have a deadline of June 30. We will adopt an extension for glyphosate of 18 months," the health commissioner told a news conference.

In the absence of any extension, manufacturers would have to phase out products containing the common herbicide within six months.

Commission sources, speaking on condition of anonymity, said a written procedure was been launched on Tuesday and the adoption was expected to be finalised on Wednesday.

After months of lobbying and member state indecision, the Commission replaced a previous proposal to renew the license for glyphosate for up to 15 years with a suggested 12 to 18 month extension pending further scientific study.