Shares in South Korean automakers rallied on Wednesday after U.S. President Donald Trump said the U.S. and Japan had struck a trade deal that includes a 15 per cent tariff that will be levied on Japanese exports to the United States.

The trade deal that US President Donald Trump celebrated as the largest in history becomes the more puzzling the more layers are peeled back. The centerpiece is Tokyo’s pledge to set up a $550 billion US investment fund and the lack of detail is raising questions about the viability of an agreement that’s been floated as a potential template for other major trading partners.

Japan's government said on Friday that profits from a $550 billion investment package agreed in this week's tariff deal with the U.S. would be split between Japan and the U.S. according to the degree of contributions by each side.