EU nations refused to back a limited extension of the herbicide glyphosate's use on Monday, threatening withdrawal of Monsanto's Roundup and other weed-killers from shelves if no decision is reached by the end of the month.

Contradictory findings on carcinogenic risks have thrust the chemical into the center of a dispute among EU and U.S. politicians, regulators and researchers. Citizen and environmental groups have urged governments to exercise caution.

The EU executive had offered a 12- to 18-month extension to allow time for further scientific study by the European Chemicals Agency (ECHA), in hopes of allaying health concerns. Its earlier proposal to renew the glyphosate license for up to 15 years had failed to win support in two meetings this year.

The compromise proposal failed to win the qualified majority needed for adoption, an EU official said, adding the European Commission will discuss the issue at a meeting on Tuesday.

Seven member states abstained and 20 backed the proposal, a German environment ministry spokeswoman said. Only Malta voted against, diplomats said.

Without a majority decision that meets the required percentage of total EU population, the EU executive may submit its proposal to an appeal committee of political representatives of the 28 member states within a month. If there is again no decision, the European Commission may adopt its own proposal.

Monsanto on Monday defended the safety of its widely used herbicide, and said glyphosate's license should be renewed for the full 15 years.

"Further delays in this process represent a significant deviation from the EU regulatory framework and set a concerning precedent for other active substances," Philip Miller, Monsanto's vice president of global regulatory and government affairs, said in a statement.