BEIJING/SHANGHAI, May 30, 2018 (News Wires) - China lashed out on Wednesday at renewed threats from the White House on trade, warning that it was ready to fight back if Washington was looking for a trade war, days ahead of a planned visit by US Commerce Secretary Wilbur Ross. In an unexpected change in tone, the United States said on Tuesday that it still held the threat of imposing tariffs on $50 billion of imports from China unless Beijing addressed the issue of theft of American intellectual property. Washington also said it will press ahead with restrictions on investment by Chinese companies in the United States as well as export controls for goods exported to China. Its tougher stance comes as President Donald Trump prepares for a June 12 summit with North Korean leader Kim Jong Un, whose key diplomatic backer is China, and as Washington steps up efforts to counter what it sees as Beijing's efforts to limit freedom of navigation in the South China Sea. The trade escalation came after the two sides had agreed during talks in Washington earlier this month to find steps to narrow China's $375 billion trade surplus. Ross is expected to try and get China to agree to firm numbers to buy more US goods during a June 2-4 visit to the Chinese capital.