The renewed U.S.-China trade truce struck in London left a key area of export restrictions tied to national security untouched, an unresolved conflict that threatens a more comprehensive deal, two people briefed on detailed outcomes of the talks told Reuters.

China’s ability to deny the U.S. defense industry the materials it needs is a powerful negotiating tool, and impacts U.S. military preparedness against China’s increasingly aggressive power projection in the Indo-Pacific.

China has leverage it can use by limiting access to its rare earth supplies, but it does not want to sacrifice its reputation as a reliable supplier.