Experts have said they believe there is a great deal of gas trapped in rock layers under German soil. Its extraction could help Germany meet its entire gas needs for 13 years, but the process of getting it out of the ground is complicated. The little bubbles of gas are trapped in layered formations of rock and in coal seams, often several thousands of meters underground.

Fracking technology uses a mixture of water, sand and chemicals that is injected under high-pressure into the rock, thereby creating fine fissures through which the gas can escape. The United States, for its part, has expanded fracking activities on a large scale.

The extraction method could mean employing, per square kilometer, "several thousands tons of partially toxic chemicals that could put health and the environment at risk,"a new report presented by the country's Federal Environmental Agency (UBA) and the Environment Ministry said on Thursday.

An interdisciplinary team of experts involved in the report focused in particular on the effects of fracking on ground water and potential contamination of drinking water, but they also concluded that more scientific data were required. Current information was insufficient "to make a conclusive assessment of possible risks," the panel said.

For German Environment Minister Peter Altmaier, that means "all concerns must be ruled out before fracking can be utilized." Experts in the study did not demand a complete ban on fracking in Germany, but suggested tight restrictions and a step-by-step approach be applied "in any specific plan, closely monitored by officials and scientists."

"Complete data should be made available about the chemicals used, their amount and their characteristics," the panel said.

For any specific fracking plan, an environmental impact assessment should be completed, experts added. The assessment would include contributions from both the initiator of the plan and the public. However, the group stressed that fracking should be outlawed in spa regions and designated areas tapped for drinking water.

To push through the requirements, the panel of experts said it would like to see overall control of the authorization process for drilling in the hands of the environment minister - an appeal Altmaier has not rejected. The mining authorities that have been responsible for overseeing the process so far are part of Germany's individual state governments. It was to them that Altmaier was addressing his admonition when he said those involved should first "thoroughly evaluate the report" presented Thursday and wait for the outcome of an expert forum involving the Environment Ministry and the Federal Environmental Agency planned for December.

No authorization until now

German states have been lukewarm on fracking up to now anyway. Several corporations have managed to gain exploration licenses in various states over the past few years. In the state of state of North Rhine-Westphalia, for example, the rights encompass 60 percent of the state's surface area, according to a risk assessment study to be presented Friday by the state government, according to the dpa press agency. However, no drilling rights have been granted yet, the agency said.