The US and the EU on Tuesday raised the stakes in a growing dispute with China, lodging a joint case at the World Trade Organisation over export quotas on raw materials. It is the latest sign of rising trade friction following the two countries’ controversial “Buy American” and “Buy Chinese” provisions, and US complaints over China’s rules on PC sales. In a co-ordinated filing, the EU and US complained to the WTO that China’s export duties on raw materials were distorting the global market.