The scramble in recent weeks to secure export licences for rare earths shows China has devised a better, more precisely targeted weapon for trade war.

China mines about 70% of the world's rare earths but has a virtual monopoly on refining and processing. Even if the pace of export approvals quickens as Trump suggested, the new system gives Beijing unprecedented glimpses of how companies in a supply chain deploy the rare earths it processes, European and U.S. executives have warned.

China views its rare earths as a national security issue, not a trade one, and that’s why Beijing is unlikely to loosen controls any time soon, experts say.