By Jeff Mason and Leika Kihara WASHINGTON/TOKYO (Reuters) -Powerhouse Asian economies Japan and South Korea said on Tuesday they would try to negotiate with the U.S. to soften the impact of sharply higher tariffs that President Donald Trump now plans to impose from the start of August.

President Donald Trump on July 7 threatened to impose 25 percent tariffs on Japan and South Korea, and levies as high as 40 percent on 12 other countries, if they did not reach a deal by August 1.

The Yale Budget Lab noted that the letters sent Monday would hike the effective tariff rate on U.S. consumers to the highest since 1934.