The European Union on Tuesday put off a decision on whether to extend approval for glyphosate, used in herbicides including Monsanto's Roundup, after a dispute between EU and U.N. agencies over whether it causes cancer.

Experts from all 28 member states attended a closed-door meeting on Monday and Tuesday in Brussels, which had been expected to endorse a European Commission proposal to extend authorisation of glyphosate for 15 years until 2031, EU diplomats said.

Commission sources said the meeting stopped short of a vote and the discussion would continue at another session of the committee on May 18-19, or possibly before.

Already on Monday, it had become clear a decision was very unlikely after France said last week it was opposed to approval of glyphosate and diplomats said the EU's biggest power, Germany, planned to abstain from any vote.

The Commission has said it needs a decision over the coming weeks to prevent a legal vacuum when an existing approval expires at the end of June.

Before the meeting, the European Food Safety Authority, which advises EU policymakers, issued an opinion that glyphosate was unlikely to cause cancer. But the World Health Organization's International Agency for Research on Cancer (IARC) has classified glyphosate as "probably carcinogenic to humans."

Environmental campaigners have called for a ban. "As long as there is conflicting scientific advice, glyphosate should not be approved for use in the EU," Greenpeace EU food policy director Franziska Achterberg said.

A statement on the website of Monsanto, which calls Roundup the flagship of its agro-chemicals business, said it strongly disagrees with the IARC's classification. It has filed a legal challenge in the United States.

The Glyphosate Task Force, which brings together Monsanto and other companies, said there had been a rigorous assessment of consumer safety and it expected approval in the coming weeks.