The United States has finalized a ban on the acquisition of tantalum metals and alloys from North Korea, China, Russia, and Iran.

The U.S. Department of Defense, which had imposed a provisional ban since October 2020, has adopted the rule as final.

The department plans to announce the move in the Federal Register on Thursday.

The Pentagon said that reducing U.S. dependence on tantalum from the four countries is a matter of national security because the chemical element is an important part of the supply chain in the production of military and non-military systems used by the Defense Department.

Tantalum is a rare and hard metal that is often used to coat jet engines and other equipment exposed to extreme heat.