China has tightened export controls on rare earths and other materials critical for advanced tech manufacturing. BBC News reports that the materials, which go into everything from solar panels to smartphones, represent a key bargaining chip in the expected upcoming meeting between Chinese leader Xi Jinping and U.S. President Donald Trump later this month.

Under the new restrictions, foreign companies now need the Chinese government's approval to export products with even small amounts of rare earths, and must explain their intended use. China had already added several rare earths and related material to its export control list in April, causing a major global shortage.

Additionally, there are restrictions on the export of lithium batteries and some forms of graphite, which are also essential components in the global tech supply chain and largely produced in China. 

Beijing said the regulations are intended to "safeguard national security." One of the main targets of these controls appears to be overseas defense manufacturers, including those in the U.S., who rely on rare earths from China.