2018.03.0821:33:00UTC+00Wall Street Advanced after Trump Signs Tariff that Exempts Mexico, Canada

U.S. stocks rose on Thursday after President Donald Trump implemented steel and aluminum import tariffs that excluded Canada and Mexico, two key U.S. trade partners.

The Dow Jones industrial average ended 93.85 points higher at 24,895.21. The S&P 500 closed 0.45 percent higher at 2,738.97, with utilities and consumer staples as the best-performing sector. The Nasdaq composite rose 0.4 percent to 7,427.95.

The major averages alternated between gains and losses throughout the session.

The tariffs signed by Trump will take effect in 15 days and will exempt Canada and Mexico indefinitely. They also leave the door open for other countries to argue why they should also be exempt. The moves slap 10 percent and 25 percent charges on aluminum and steel imports, respectively.

Ahead of the news that came out from the White House in the last hour and a half of the trading day, the S&P had fluctuated in a tight range between positive and negative territory as investors were uncertain about what Trump would say.

Worries that the tariffs would ignite a global trade war have dominated markets since he announced the tariff plan, and the exit of chief economic adviser Gary Cohn intensified the concerns.

Shares of U.S. Steel and Nucor fell 2.9 percent and 2.7 percent, respectively, while Century Aluminum fell 7.5 percent. Boeing, a large metals user, saw its shares increase 0.5 percent.

Investors also looked ahead to the release of the Bureau of Labor Statistics' monthly jobs report.

In corporate news, Cigna announced it plans to buy Express Scripts for $67 billion in a cash-and-stock deal. Cigna would find a new partner in Express Scripts, after antitrust regulators last year denied a Cigna and Anthem combination as anti-competitive. Express Scripts shares rose more than 8 percent on the news.