US biotech giant Monsanto scored points Thursday in a battle with GM sceptics in the EU, when Europe's highest court warned against fresh unilateral action against genetically-modified crops.

In a ruling targeting France in particular, the European Court of Justice said EU states in the future must notify the European Commission before banning GM crops.

They must moreover provide evidence "of a situation which is likely to constitute a clear and serious risk to human health, animal health or the environment", the court added.

The decision stems from a long-running bid by Monsanto to overturn a 2008 ban by France on genetically-modified MON 810 maize. But six other nations too have banned Monsanto maize -- Austria, Bulgaria, Germany, Greece, Hungary and Luxembourg.

The ruling, which is not legally binding, is to go before France's highest administrative court for consideration.

But should the court, the Council of State, ratify the Luxembourg-based court's decision, the government will have to scrap its so-called "safeguard clause" against GM crops.

Environmental campaigners responded angrily to the move and French Environment Minister Nathalie Kosciusko-Morizet wasted no time in warning that should the ban be overturned by the court, "we will introduce a new safeguard clause".

"The European Court of Justice at no time raised the environmental and health risks posed by GMs. It simply raised concerns over procedure," said Greens' European parliamentarian Jose Bove.

"We risk seeing GMs back in our fields from next spring," said Greenpeace France director Sylvain Tardy.

GM lobby EuropaBio predictably welcomed the ruling "as a step towards choice in Europe."

"French farmers should no longer be denied the choice to use this GM maize," it said in a statement.

The European Court of Justice's opinion follows a series of battles between European Union nations with a distaste for GM crops and the biotech industry, and comes two days after a key ruling on honey containing traces of GM pollen.

The European Commission has been willing to let individual EU states ban GM crops, on certain grounds designed to get round World Trade Organization rules, but only if Brussels is notified first.

MON 810, which is used for animal feed and is resistant to certain parasites, is one of only two GM crops to have been authorised in the 27-nation European Union. The other is German group BASF's Amflora potatoes, used to make paper.

The EU top court said that while France could adopt emergency measures, it should have applied a different set of EU rules.

"The member state must therefore inform the commission 'officially' of the need to take emergency measures," the court said.

"If the commission fails to act, the member state must inform it and the other member states 'immediately' of the content of the interim measures which it has adopted," it said.

In a separate ruling Tuesday, the court said that honey containing even tiny traces of pollen from GM maize could not be sold in the EU without prior authorisation.