(Adds French reaction)
LUXEMBOURG, Sept 8 (Reuters) - France acted illegally when it imposed a ban on the cultivation of a genetically modified (GM) maize variety developed by U.S. biotech giant Monsanto in 2008, Europe's highest court ruled on Thursday.
The French authorities did have the right to impose a moratorium on the growing of Monsanto's insect-resistant MON810 maize, but based its decision on the wrong EU legislation, the Luxembourg-based European Court of Justice said.
In reaction to the ruling, France said its embargo on MON810 maize was still valid and that it would restart a procedure if needed.
To impose such a ban, member states must demonstrate a potentially serious risk to human or animal health or the environment, and notify EU authorities of the need to take emergency measures, the court said.
Emergency measures must be based on science and backed by an assessment from the European Food Safety Authority (EFSA), according to the European Commission.
France imposed its safeguard clause against MON810 maize in February 2008, citing a "serious risk to the environment."
Six other EU countries -- Germany, Austria, Bulgaria, Greece, Hungary and Luxembourg -- have similar safeguard clauses in place.
Having tried and failed to force several EU countries to lift their cultivation bans, last year the Commission proposed letting member states decide themselves whether to grow or ban GM crop cultivation.
A spokesman for EU health and consumer commissioner John Dalli said talks on the proposal would continue, but France would have to abide by the court's ruling.
"It's now up to the French administrative court to decide whether to table a new safeguard clause," the spokesman said.
French Environment Minister Nathalie Kosciusko-Morizet said the EU decision did not mean the end of France's ban on the MON810 maize.
"If the French clause was annuled for procedure reasons, we would take a new safeguard clause under a procedure considered adequate by the European Court of Justice, because environmental questions remain unanswered," she said in a statement.
A spokesman for Monsanto said the ruling confirmed its argument that the French authorities failed to follow the correct procedures when imposing the ban.
"Over the last 15 years, MON810 has proven agronomic, economic and environmental benefits and its safety has been confirmed consistently. French farmers should no longer be denied the choice to use it," he said. (Reporting by Charlie Dunmore and Julien Toyer, additional reporting by Sybille de La Hamaide, editing by Rex Merrifield)