Chinese exports of rare earths—17 key minerals at the heart of trade tensions with Washington—rose 23% in May compared to the previous month, customs data showed Monday. May shipments totaled 5,865 tons—still below last year’s level—but the monthly surge lifted year-to-date exports by 2.

The US trade war with China has a major sticking point: rare earths minerals. Last month, President Donald Trump said the United States needed Greenland “very badly,” renewing his threat to annex the Danish territory.

The United States and China will resume high-level trade talks in London on Monday to ease disputes over rare-earth minerals and advanced technology after