BRUSSELS - European Union (EU) leaders in a summit meeting on Thursday night warned the United States that "all actions of a clear protectionist nature" would prompt retaliation.

"In reaction to the United States' decision to impose tariffs on the EU for steel and aluminium products, which cannot be justified on the grounds of national security, the European Council fully supports the rebalancing measures, potential safeguard measures to protect our own markets, and the legal proceedings at the WTO, as decided on the initiative of the commission," read the summit conclusions issued on early Friday.

"The EU must respond to all actions of a clear protectionist nature, including those calling into question the Common Agricultural Policy," it added.

The United States started imposing tariffs of 25 percent on steel imports and 10 percent on aluminium from the EU, Canada and Mexico on June 1.

The imposition of the new tariffs has been viewed as "pure protectionist" by the EU. The EU's retaliatory tariffs on a list of US products valued 2.8 billion euros ($3.26 billion), ranging from motorcycles to orange juice, came into effect on June 22.

US President Donald Trump is also threatening to impose tariffs on EU cars and auto parts within months, which, if put into place, would hit the EU and Germany in particular much harder than the metal tariffs did.