European Union negotiators were scrambling for details on the weekend, after United States President Donald Trump threatened to increase the tariff on cars and trucks imported from the bloc, from the current 10 percent to 25 percent.

Trump announced the move on Friday in a social media post in which he claimed the EU was "not complying with our fully agreed to Trade Deal".

With his characteristic overuse of capital letters, Trump wrote: "I am pleased to announce that … next week I will be increasing Tariffs charged to the European Union for Cars and Trucks."

He did not say how the 27-nation bloc of European nations had failed to comply with the terms of their trade deal, but said the new higher tariff would motivate it to make changes.

"It is fully understood and agreed that, if they produce Cars and Trucks in U.S.A. Plants, there will be NO TARIFF," Trump wrote.

In response to reporters' questions on Friday, he added that the EU had consistently failed to abide by last year's trade deal, and that the new tariff "forces them to move their factory production much faster".

Currently, most exports from the EU to the US are subject to a 10 percent tariff that Trump's administration hastily introduced after the US Supreme Court struck down the previous 15 percent tariff that was in place for most imports from the EU under the terms of their trade deal.

The Supreme Court said Trump did not have the legal authority to impose such a tariff without the approval of lawmakers.

Trump and European Commission President Ursula von der Leyen had previously agreed a trade deal last July that many Europeans complained was lopsided, because it called for a zero percent tariff on US exports to the EU and a 15 percent tariff on EU exports to the US. The deal also called for EU companies to shift some production to the US.

The EU responded to Trump's announcement of a higher tariff for automobiles by saying the bloc would continue to follow its "commitments in line with standard legislative practice" and that, if Washington takes "measures inconsistent with" the trade deal they reached, the bloc would "keep our options open to protect EU interests".

The statement added that it was seeking "clarity" about Trump's latest threat.

Bernd Lange, chair of the European Parliament's international trade committee, wrote on social media that a higher tariff on vehicles was "unacceptable" and that the US administration "keeps breaking its commitments".

He said the US side had made similar moves against EU steel and aluminum products.

Kyriakos Pierrakakis, president of the Eurogroup, the informal association of Eurozone finance ministers, said Europe is ready to respond should Trump follow through on his threat.

"The number one choice is always dialogue — we want to be a predictable partner in the international economy, we believe in the transatlantic relationship," he told Bloomberg Television.

"But having said this, if there is a deviation from what we have agreed upon, obviously all options are on the table and all choices will be on the table."

The BBC said Trump's latest move will have escalated tension between the two sides, which shared trade worth $2 trillion in 2024, according to the EU's statistics agency Eurostat.