Speaking to the Senate Finance Committee, Lighthizer said those exempt are Argentina, Australia, Brazil, South Korea, and the EU.
Washington had already granted exemptions to Canada and Mexico as renegotiations over the North American Free Trade Agreement continues.
Lighthizer said that there are countries involved in various stages of trade talks with the United States and that the president decided "to pause the imposition of tariffs with respect to those countries."
Amid widespread dissent from business groups and trading partners around the world, Trump signed two weeks ago proclamations to impose a 25-percent tariff on imported steel and 10-percent on aluminum, which take effect on Friday.
Many economies have warned the White House that they will retaliate if they are faced with tariffs on metals products.
EU Trade Commissioner Cecilia Malmstrom said that the economic bloc is "always willing to engage with our American partners, but we do not negotiate anything under pressure or threat."
It was one of Trump campaign promises to bring down the country's trade deficit, which totaled 566 billion U.S. dollars in 2017.
However, economists say that the tariffs are unlikely to bring the U.S. current account into balance as the major cause of the trade imbalance lies in the fact that the U.S. savings are low relative to investment.