WASHINGTON — A group of US medical professionals called Monday for a halt to a type of drilling for natural gas called "fracking" in populated areas until more is known about its health impacts.

"When it comes to hydrofracking, our guiding principle for public policy should be the same as the one used by physicians: 'First, do no harm,'" said Adam Law, of Weill Cornell Medical College, and a founding member of Physicians Scientists and Engineers for Healthy Energy.

"There is a need for scientific and epidemiological information on the health impacts of fracking. Frankly, no one should be unleashing even more fracking before we have the scientific facts. There are health care needs in various gas drilling communities and these must be met. The reality is that industry has not done nearly enough to finance the needed research effort."

The comments came at a conference called in response to a suggestion made by the National Institute of Environmental Health Sciences the health implications of fracking -- which uses high pressure injections of water, sand and chemicals are used to blast through rock to release oil and gas trapped inside.

The technique has been used to vastly boost US natural gas output, but some critics express concern that it may lead to groundwater contamination and other environmental impacts.

"There are a lot of questions related to the human health and ecological impacts of this process of unconventional gas extraction that need to be answered," said Jerome Paulson of the George Washington University School of Medicine & Health Sciences.

"The answers to the questions about the human and ecosystem health impacts here will only come from scientific research."

Chris Tucker, spokesman for the industry-backed group Energy In Depth, said the gathering was not a conference of concerned scientists, it?s a conference of paid activists."

"We've been fracturing wells in this country since the Truman administration, more than 1.2 million applications over 65 years in more than 30 different states," Tucker said in an email.

"What these guys are essentially arguing is that the mere act of turning a drill bit horizontally... represents a greater risk to human health than drilling straight down into the formation, which we've been doing safely for more than 150 years. It's a position that's completely unmoored from the facts, from the science, and from the demonstrable history of safe operations to which this industry lays claim."