By Jasper Ward and Jeff Mason

(Reuters) -The U.S. tariff rate on most imported steel and aluminum will double on Wednesday as President Donald Trump ratchets up a global trade war on the same day he expects trading partners to deliver their "best offer" in bids to avoid punishing import tax rates on other goods from taking effect in early July.

Trump late Tuesday signed an executive proclamation that puts into effect from Wednesday his surprise announcement last week that he was taking the tariffs on steel and aluminum imports that had been in place since March to 50% from 25%.

"We started at 25 and then after studying the data more, realized that it was a big help, but more help is needed. And so that is why the 50 is starting tomorrow," White House economic adviser Kevin Hassett said

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