Greenpeace activists Friday unloaded a truck of maize outside the Paris headquarters of French presidential candidate Nicolas Sarkozy, urging him to back a moratorium on genetically-modified crops. The environmental group told AFP it targeted Sarkozy, head of the right-wing ruling UMP party, because he was "the only candidate in the presidential election who has not backed a moratorium on open-field GM crops." Fourteen protestors were arrested for holding an unauthorised demonstration and briefly held for questioning, Paris police said.

Sarkozy's Socialist rival Segolene Royal has promised an immediate moratorium on GM crops -- opposed by a majority of the French public -- if she is elected in the April-May vote.

The centrist Francois Bayrou, in third place in the polls, has also said he backs a moratorium to allow for a national scientific debate on the question.

France's Green Party campaigns actively against GM crops, while the farmer-activist Jose Bove has served several jail sentences for ripping them up.

Sarkozy has said he is "sceptical about the real benefits of GMOs" but that open-field crop trials should continue for research purposes, to keep open the option of using GM crops "once all safety conditions have been met."

Opponents of the crops argue that their health and environmental impact is not yet fully understood, and warn of a risk of pollen contamination to conventional and organic farm produce.

According to French government figures, 23.19 hectares (57 acres) of open-field crops were cultivated for research purposes in 2005.

GM maize is the only commercial GM crop authorised in France, with some 500 hectares (1,235 acres) declared by farmers in 2005 compared to three million hectares for conventional maize.