The United States will file a new trade case against China over its limits on exports of so-called rare earth minerals. Officials said President Barack Obama will announce today that the US, along with the European Union and Japan, will file the case at the World Trade Organization. China is the world's main exporter of rare earths – 17 minerals used in making many high-tech products including flat screen televisions, hybrid car batteries and wind turbines. China says it has restricted the exports in recent years in order to meet its own domestic manufacturing needs, and to ease the environmental impact from excessive mining.