WASHINGTON – The US has expanded its challenge at the World Trade Organisation to China's exportrestraints on raw materials to include export duties on chromium, as well as its export quotas on antimony, indium, magnesia, talc and tin, the US Trade Representative (USTR) said on Tuesday.

Those raw materials "are key inputs into high-value US-madeproducts in vital industrial sectors, including aerospace,automotive, construction and electronics. China's exportrestraints on these materials, including duties and quotas, provide an unfair competitive advantage to China at the expense of American workers and manufacturers," the USTR said in a statement.