BRUSSELS (AFP) – France broke the law when it halted cultivation of genetically-modified crops without first asking the EU to impose emergency measures, the legal advisor to Europe's top court said on Tuesday.

Advocate-general Paolo Mengozzi's opinion represents a major blow to France, Austria, Greece and Poland, all of whom sought European Court of Justice guidance after being taken to court in national jurisdictions by GM-foods giant Monsanto and others.

"The French authorities could not suspend the cultivation of genetically-modified maize MON 810 on national territory without having first asked the European Commission to adopt emergency measures citing a risk to health and the environment," Mengozzi said.

Judges are not bound by the legal opinion, but in the vast majority of cases the legal argument holds firm.

The advocate-general also said France cannot now invoke a safeguard clause inserted into European Union law aimed at preventing the release of GM cells into the environment.

The MON 810 strain, which the court said is "particularly resistant to parasites and used as animal feed," was first authorised in 1998.

In 2007, Monsanto applied for re-authorisation, valid for 10 years, but France adopted national laws in December that year and February 2008 outlawing its growing, amid public outcry in a famously proud traditional farming nation over the march of GM crops.

The safeguard clause, however, may not be invoked by states on their own, and besides, in this instance, the company was not informed of the legal basis for its exclusion from the French market -- which the court also said was the wrong legal basis.

It should have been based on law covering raw material foodstuffs and genetically-modified animal feed, and only the European Commission can make that call, the court said, because only Europe-wide action could act sufficiently to protect health and the environment.