Gilles-Eric Seralini of the University of Caen and colleagues said on Wednesday that rats fed on Monsanto's genetically modified corn or exposed to its top-selling weed killer suffered tumors and multiple organ damage and premature death.

But experts not involved with the study were skeptical, describing the French team's statistical methods as unconventional and accusing them of going "on a statistical fishing trip".

Speaking at a news conference in Brussels on Thursday, Seralini defended the peer-reviewed study, which was published in the journal Food and Chemical Toxicology.

"This study has been evaluated by the world's best food toxicology magazine, which took much more time than people who reacted within 24 hours without reading the study," he told Reuters Television.

"I'm waiting for criticism from scientists who have already published material in journals... on the effects of GMOs and pesticides on health, in order to debate fairly with peers who are real scientists, and not lobbyists."

Earlier, the European Commission said it had asked the EU's food safety authority, EFSA, to verify the results of the French study and report their findings.

"EFSA's mandate is to verify what this group of scientists has presented, to look at their research conditions, look at how the animals were treated," Commission health spokesman Frederic Vincent told a regular news briefing.

"We hope that by the end of the year we will have an EFSA opinion on this piece of scientific research."

In 2003, EFSA published a safety assessment of the GM corn variety known as NK603, which is tolerant to Monsanto's Roundup weed killer. The assessment concluded that NK603 was as safe as non-GM corn, after which the European Union granted approval for its use in food and feed.

Seralini said EFSA's assessments were less rigorous than his team's study.

"GMOs have been evaluated in a extremely poor and lax way with much less analysis than we have done. It's the world's most detailed and longest study. Therefore, some people are responsible and guilty of authorizing this GMO after only three months," he said.

(Reporting by Clement Rossignol; Writing by Charlie Dunmore; Editing by Hugh Lawson)

• A Permanent Economic Emergency