Each F-35 fighter jet contains roughly 900 pounds of rare earth materials, while submarines can require more than 9,000 pounds, the U.S. Department of Defense has concluded a stark reminder of how deeply integrated these elements have become in the machinery of modern defense.

China has granted temporary export licenses to rare-earth suppliers of the top three U.S. automakers, two sources familiar with the matter said, as supply chain disruptions begin to surface from Beijing's export curbs on those materials.

A group representing auto suppliers in the United States called on Wednesday for immediate action to address China's restricted exports of rare earths and other minerals, warning the issue could quickly disrupt auto parts production.