BRUSSELS - The European Commissioner for Trade and Economic Security Maros Sefcovic said Tuesday that the European Union (EU) will respond "firmly and proportionately" to the tariffs imposed by the United States.

"We deeply regret this. In our opinion the tariffs are unjustified, because they will lead to an increase in prices and inflation," Sefcovic said in a speech to members of the European Parliament (MEPs) in Strasbourg.

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Describing the move as a "lose-lose scenario," he warned that the tariffs were "economically counterproductive," but emphasized the EU's willingness to engage in a "constructive dialogue."

"We will keep all communication channels open. The EU is ready for any challenges that may arise in the field of trade. When necessary, we will defend our openness, industry and single market," he said.

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Earlier in the day, European Commission President Ursula von der Leyen said that US tariffs on steel and aluminum imports from the EU would "trigger firm and proportionate countermeasures."

"I deeply regret the US decision to impose tariffs on European steel and aluminum exports. Tariffs are taxes -- bad for business, worse for consumers," she said in a statement.

"Unjustified tariffs on the EU will not go unanswered," von der Leyen warned, adding, "The EU will act to safeguard its economic interests. We will protect our workers, businesses and consumers."

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US President Donald Trump announced Monday that steel and aluminum imports would be subject to a 25-percent tariff upon entering the United States, regardless of their country of origin.