Sri Lanka, Feb. 11 -- U.S. President Donald Trump substantially raised tariffs on steel and aluminum imports on Monday to a flat 25% "without exceptions or exemptions" in a move he hopes will aid the struggling industries in the United States but which also risks sparking a multi-front trade war.

Trump signed proclamations raising the U.S. tariff rate on aluminum to 25% from his previous 10% rate and eliminating country exceptions and quota deals as well as hundreds of thousands of product-specific tariff exclusions for both metals. A White House official confirmed the measures would take effect on March 4.

The tariffs will apply to millions of tons of steel and aluminum imports from Canada, Brazil, Mexico, South Korea and other countri...