U.S. military aid for developing Ukraine's mineral industry, a potential source of rare elements used in technology.

China, with whom Trump has threatened a trade war, is the world's largest producer of rare earths and many other critical minerals. Both the U.S and Europe have sought to reduce their dependence on Beijing.

Donald Trump has said Ukraine “may be Russian someday” as senior figures in his administration prepare to meet with Volodymyr Zelensky this week.