WASHINGTON  -- The United States on Monday formally exempted South Korea from steep tariffs on steel imports, saying the move was in line with national security interests.

US President Donald Trump earlier announced a 25 percent tariff on steel imports and a 10 percent tariff on aluminum imports from all countries in principle, citing the need to protect the nation from what his administration called a threat to national security.

"Today, President Donald J. Trump issued two proclamations authorizing modifications of the Section 232 tariffs on steel and aluminum," the White House said in a statement. "The Administration has reached a final agreement with South Korea on steel imports, the outlines of which were previously announced by US Trade Representative Robert Lighthizer and Republic of Korea Minister for Trade Hyun-chong Kim." 

The agreement calls for an annual import quota of 2.68 million tons while granting the exemption. The quota amounts to 70 percent of the average of steel exports to the US over the last three years.

The deal was reached last month as the two countries also negotiated an amendment to their free trade agreement. The revised version has yet to be signed and gives US automakers greater access to the South Korean market.

"In my judgment, these measures will provide an effective, long-term alternative means to address South Korea's contribution to the threatened impairment to our national security by restraining steel articles exports to the United States from South Korea, limiting transshipment, and discouraging excess capacity and excess steel production," Trump said in the proclamation on steel.

"In light of this agreement, I have determined that steel articles imports from South Korea will no longer threaten to impair the national security and have decided to exclude South Korea from the tariff proclaimed in Proclamation 9705," he said, adding the US will monitor the quota's implementation and "may revisit this determination, as appropriate."

South Korea will still be subject to the tariff on aluminum. (Yonhap)