"The committee cannot say anything but that there are serious doubts on the use of MON 810," the head of the committee, senator Jean-Francois Legrand, told a joint news conference with French Environment Minister Jean-Louis Borloo.

Monsanto was not immediately available for comment.

French President Nicolas Sarkozy said on Tuesday that if the experts expressed "serious doubts" over GMO use, he would use a safeguard clause which allows European Union members to refrain from applying EU laws on the basis they may put the population at risk.

Borloo said Sarkozy would make a decision based on the report within 48 hours.

Last month France imposed a temporary ban on the commercial sale of MON 810 maize until February 9, to allow time to look into the environmental and health implications of its use.

However, the suspension did not have an immediate effect on crops because maize sowings only take place in the spring.

If France decides to use the safeguard clause, it would have to provide the European Commission, the EU's executive body, with proof that there is new scientific evidence justifying a ban on the genetically modified MON 810 maize.

The Commission would then have 60 days to decide on the validity of France's argument. If the Commission deemed it invalid, France would probably receive an order to lift its ban.

Legrand said the committee found new evidence arguing against the safety of the maize, including much wider dissemination than had been acknowledged in 1998 when the EU had evaluated it, as well as a negative impact on biodiversity.

The EU has approved the use of Monsanto's MON 810 technology around the 27-nation bloc, but several countries including France and Germany have expressed concern about its safety.

Germany agreed last month to lift its temporary ban on the maize after Monsanto agreed to extra crop monitoring there.