The Trump administration has ordered a halt to an independent study looking at potential health risks to people living near mountaintop mining sites in Appalachia.

The U.S. Department of Interior's Office of Surface Mining Reclamation and Enforcement sent a letter to the National Academy of Sciences on Friday instructing it to cease all work on the study.

The study had been launched at the request of two West Virginia agencies, the state's Department of Environmental Protection and Bureau for Public Health.

The agencies sought federal assistance with a research review after several dozen scientific papers found increased risks of birth defects, cancer and premature death among residents living near large-scale surface coal mines in Appalachia. The Office of Surface Mining had committed $1 million to the study under President Obama in 2016.

The letter calling for an end to that study stated that the Department of Interior "has begun an agency-wide review of its grants and cooperative agreements in excess of $100,000, largely as a result of the department's changing budget situation," the National Academy of Sciences said in a statement.

The Interior Department has drawn criticism for moves seen as silencing scientific expertise. Interior Secretary Ryan Zinke froze several science advisory boards earlier this year, and a prominent Interior Department climate scientist blew the whistle on the department last month, alleging that he and dozens of other scientists had been arbitrarily reassigned. A group of senators subsequently called for a probe to investigate the reassignments.

President Donald Trump has also been touting efforts to bring back coal. He has scrapped regulations that were opposed by the fossil fuel industry, and his proposed 2018 budget would cut funding for the Office of Surface Mining, which is responsible for protecting society and the environment from the adverse effects of surface coal mining operations.

Environmental advocates and the top Democrat on the House Committee on Natural Resources denounced the shutdown of the health study.

"It's infuriating that Trump would halt this study on the health effects of mountaintop removal coal mining, research that people in Appalachia have been demanding for years," Bill Price, Senior Appalachia Organizing Representative for Sierra Club's Beyond Coal campaign, said in a statement.

"Stopping this study is a ploy to stop science in its tracks and keep the public in the dark about health risks as a favor to the mining industry, pure and simple," Raúl Grijalva (D-Ariz.), ranking member of the House Committee on Natural Resources, said in a statement.

The federally funded National Academies, whose mission is to provide "independent, objective advice to the nation on matters related to science and technology" said it will go forward with previously scheduled meetings for this project in Kentucky on August 21-23 but will await the results of the Interior Department's review before taking further action.

"The National Academies believes this is an important study, and we stand ready to resume it as soon as the Department of the Interior review is completed," the National Academies said.