U.S. President Donald Trump substantially raised tariffs on steel and aluminum imports 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, writes Reuters.

"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 countries that had been entering the U.S. duty free under the carve-outs. The move will simplify tariffs on the metals "so that everyone can understand exactly what it means", Trump told reporters. "It`s 25% without exceptions or exemptions. That’s all countries, no matter where it comes from, all countries".

Trump later said he would give "great consideration" to Australia`s request for an exemption to the steel tariffs due to that country`s trade deficit with the U.S.

The proclamations were extensions of Trump`s 2018 Section 232 tariffs to protect domestic steel and aluminum makers on national security grounds.

A White House official said the exemptions had eroded the effectiveness of these measures. Trump also will impose a new North American standard requiring steel imports to be "melted and poured" and aluminum to be "smelted and cast" within the region to curb U.S. imports of minimally processed Chinese and Russian metals that circumvent other tariffs.

The action also extends the tariffs to downstream products that use foreign-made steel, including fabricated structural steel, aluminum extrusions and steel strand for pre-stressed concrete, a White House official said.

As he signed the order at the White House, Trump said he would follow Monday`s action with announcements about reciprocal tariffs on all countries that impose duties on U.S. goods over the next two days, and said he was also looking at tariffs on cars, semiconductors and pharmaceuticals. Asked about threats of retaliation by other countries against his new tariffs, Trump said: "I don`t mind".