US President Donald Trump's administration has levied an additional 25-percent tariff on imported key auto components, including engines and transmissions.



The move came shortly after 4:00 UTC on Saturday, following his imposition of a 25-percent tariff on foreign-made vehicles on April 3.



Washington cited Section 232 of the Trade Expansion Act of 1962, which allows a president to restrict imports that threaten national security.



But the Trump administration announced earlier this week its decision to relax some of his automobile tariffs as US carmakers voice concerns. They said the tariffs could raise their production costs as they were importing parts from other countries.



The government says it will reimburse carmakers for some of the money they pay for foreign parts.



It says that in the first year, the offset will be the equivalent of 3.75 percent of the sticker price of domestically-assembled cars.



Data from Japan's Finance Ministry show that the country's auto parts exports to the US stood at 1.23 trillion yen, or about 8.5 billion dollars. The amount accounts for 5.8 percent of Japan's total exports to the US, and is the second biggest by item, following automobiles.



There is concern among Japanese parts makers that the new US tariffs could strain their businesses.