China is tightening its grip over global critical-mineral supplies by placing export controls on antimony, a metal used widely in ammunition and other military applications that’s seen a surge in prices this year. 

The country will apply the restrictions to antimony and antimony-related materials from Sept. 15 in order to safeguard national security, according to a statement from the Ministry of Commerce on Thursday. That adds to earlier controls on other critical minerals including gallium and germanium, which have set off alarm bells in Washington.

China is the world’s top supplier of more than 30 critical minerals, and it claims a 56% share of global mined supplies of antimony, according to a 2023 European Union study. That dominance has been built up over decades, but in recent years the US and other western governments have been ramping up efforts to secure alternative supplies. 

Beijing’s restrictions on critical minerals have also been viewed in part as a tit-for-tat response to the Biden administration’s increasingly aggressive efforts to keep China from gaining the upper-hand in artificial intelligence and chip manufacturing. In the latest salvo, the US is considering unilateral restrictions on China’s access to AI memory chips and equipment capable of making those semiconductors as soon as next month, Bloomberg has reported.

While China is by far the world’s top antimony miner, production has fallen substantially in recent years, in a trend that’s fueled fears of global shortages and underpinned a surge in prices. At $23,150 a ton, the metal is up nearly 100% this year and is at highest price since at least 2005, according to Fastmarkets data. The US produces no mined antimony domestically, and uses it primarily in ammunition and flame retardants, as well as ceramics, glass and rubber products, according to the US Geological Survey.

Concerns about China’s grip over critical-mineral supplies have grown sharply since it placed gallium and germanium under stricter government oversight a year ago, in a move that has sent prices for the two metals soaring. It also later put graphite under the same export scrutiny and halted outbound sales of a range of rare-earth technologies.