In September, a row broke out after researchers led by Gilles-Eric Seralini at the University of Caen in Normandy, said rats fed with the genetically-modified corn NK603, made by Monsanto, and/or doses of its Roundup weed killer, developed tumours.
On Monday, the Higher Biotechnologies Council (HCB) and the National Agency for Food Safety (ANSES) said they saw nothing to challenge existing safety assessments for Monsanto's NK603 corn or its Roundup weed killer.
"The study provides no scientific information regarding the detection of any health risk linked to NK603 corn, whether it was treated with Roundup or not," said the 66-member HCB, set up in 2009 to provide an independent view in such areas.
"The data are insufficient to establish scientifically a causal link... or to support the conclusions or pathways suggested by the authors," ANSES said separately.
But both called for a broader investigation to guide a public left confused by the debate.
The HCB said the inquiry should look further into whether NK603 had long-term impacts on health, while ANSES urged a probe into any consequences of combined exposure to NK603 and Roundup. Both issues had been explored in the study.
But critics had faulted the experimental methods and data and accused him of manipulating the media to gain scary headlines. In an exceptional move on Friday, six French science academies had said the work was flawed and had "spread fear among the public".
On Monday, Gilles-Eric Seralini said he would welcome a wider investigation but that in the meantime, NK603 should be banned.
"A two-year study takes four years to set up and analyse, and during these four years, who else is going to fall sick or die because of these poorly-tested products?" he asked.
Monsanto said at its French headquarters in Lyon that "it took note" of the HCB's findings and said the recommended probe "does not change risk assessments" for NK603.
NK603 has been engineered to make it resistant to Roundup, so that farmers can douse fields with the Monsanto weed killer in a single operation and save money.
Greenpeace said Seralini had exposed a gap in testing transgenic products for their long-term impact on health and the environment.
Seralini is a well-known opponent of GM food. But his paper appeared in the journal, Food and Chemical Toxicology, which uses the peer-review process, a system designed to ensure published research is accurate and fair.