Washington, April 3 : US President Donald Trump signed a sweeping proclamation imposing steep tariffs on imports of steel, aluminium and copper, tightening trade controls in the name of national security.

The order mandates that tariffs apply to the â??full customs valueâ?? of imported metal products and their derivatives, closing what the administration described as loopholes in earlier measures.

The move builds on earlier Section 232 actions, under which the US had already determined that rising imports of key metals â??threaten to impair the national security of the United Statesâ??.

Under the new regime, most primary steel and aluminium products will face a 50 per cent ad valorem duty, while certain derivative products will be subject to a 25 per cent tariff.

Officials said the changes are aimed at ensuring importers pay duties based on actual transaction prices rather than artificially lowered values.

â??We are going to charge 50 per cent of the full value of the steel paid by US customers in America,â?? a senior administration official said, explaining the revised methodology.

The official added that the new structure is designed to eliminate pricing distortions by exporters.

â??They were just artificially making it lower, and weâ??re just getting rid of that because they were basically fooling the system,â?? the official said.

The administration also introduced a simplified framework for derivative products. Items with limited metal content will be exempt from additional tariffs, while those with substantial metal composition will face a flat duty.

â??If itâ??s got substantial amounts of steel, aluminium or copperâ?¦ itâ??ll have a simple 25 per cent tariff,â?? the official said.

Officials argued the overhaul would streamline compliance and reduce administrative complexity for importers, while strengthening enforcement.

The proclamation states that domestic capacity utilisation in aluminium and steel has risen since the original tariffs were imposed, reaching about 50.4 per cent for aluminium and 77.2 per cent for steel.

The administration said further tightening was needed to push utilisation closer to the targeted 80 per cent and to prevent circumvention through derivative products.

In addition to tariff hikes, the order authorises US authorities to expand the list of covered products on a â??rolling basisâ?? if imports are found to undermine national security objectives.

Officials insisted the measures would not significantly affect consumer prices.

â??I donâ??t think itâ??s going to have any impact on affordability,â?? the official said, adding that the changes primarily affect trade mechanics rather than retail pricing.

The tariffs will take effect from April 6, applying to goods entering the US market from that date.

/IANS