U.S. President Donald Trump's sweeping tariffs on steel and aluminum imports went into effect Wednesday, attracting retaliatory measures from Europe.

The Trump administration imposed 25% tariffs on all steel and aluminum imports, after the U.S. and Canada backed off threats to impose additional measures Tuesday, capping a roller-coaster day on Wall Street with investors rattled by uncertainty in trade policy.

U.S. President Donald Trump's increased tariffs on steel and aluminum imports took effect on Wednesday as prior exemptions, duty free quotas and product exclusions expired, as his campaign to reorder global trade norms in favor of the U.