PARIS (Reuters) - Environmental group Greenpeace launched a fresh attack on genetically modified maize developed by U.S. biotech giant Monsanto, saying on Tuesday that rats fed on one version developed liver and kidney problems.

Greenpeace said a study it had commissioned that was published in the journal Archives of Environmental Contamination and Technology showed rats fed for 90 days on Monsanto's MON863 maize showed "signs of toxicity" in the liver and kidneys.

"It is the first time that independent research, published in a peer-reviewed journal, has proved that a GMO authorized for human consumption presents signs of toxicity," Arnaud Apoteker, a spokesman for Greenpeace France said in a statement.

Campaigners against Genetically Modified Organisms (GMO) say that genetic modification technology is unproven and potentially dangerous and that GMO crops can contaminate other crops.

The industry says the technology offers vast potential benefits, poses no health risk and has never been shown to contaminate other crops.

"All the experts agree that the maize in question is as safe as traditional maize," Yann Fichet, director external relations for Monsanto France told France's TF1 television.

He said the maize had been authorized in more than 10 countries and in the European Union but he declined to comment specifically on the allegations raised by Greenpeace.

MON863 is a form of maize genetically modified to make it resistant to corn rootworm. It has been authorized by the European Union for use in animal feed since 2005 and for human consumption since January 2006.