The newly announced limits also cover super-hard materials, such as diamonds and other synthetic materials that are not compressible and extremely dense, reports AP. These are used in cutting tools, disc brakes and protective coatings.

"To safeguard national security interests and fulfil international obligations such as non-proliferation, China has decided to strengthen export controls on relevant dual-use items to the United States," China's Commerce Ministry said.

China accounts for 94% of the world's production of gallium, and 83% of germanium. Exports of the two materials from China to the US had fallen to zero following the introduction of restrictions last year.