United States President ​Donald Trump on Friday ‌said he would be increasing tariffs on cars and trucks ​from the European Union ​to 25%, saying the bloc had ⁠not complied with its ​trade deal.

"Based on the ​fact the European Union is not complying with our fully agreed ​to trade deal, next ​week I will be increasing tariffs ‌charged ⁠to the European Union for cars and trucks coming into the United States," he ​wrote ​in ⁠a social media post.

"It is fully understood ​and agreed that, if ​they ⁠produce cars and trucks in USA plants, there will ⁠be ​no tariff," Trump ​added.

Read More: Trump's attacks on Europe's leaders worsen transatlantic frost

In his post, Trump also emphasised manufacturing automobiles in the US.

“Many automobiles and truck plants are currently under construction, with over 100b dollars being invested," he added.

Trump told reporters at the White House that the higher tariff would force European car ​makers to move their factory production to the US more quickly.

"We have a trade deal with the European Union. They were ​not adhering to it. So I raised the tariffs on cars and trucks to 25%, that's billions of dollars coming into the United States, and it forces them to move their factory production much faster."

The past weeks have not been reassuring for those who thought Europe could navigate its tricky relationship with Trump.

The Trump administration last year imposed a 25% tariff on global automotive imports under a national ​security trade law, but reached a deal with the EU in August to lower those duties to a net 15%, ​inclusive of prior duties.

In exchange, the EU agreed to eliminate duties on US industrial goods, including autos, and accept US safety and emissions ‌standards ⁠on vehicles.

Although EU lawmakers advanced legislation in March to implement the tariff reductions, the process is not expected to be completed before June, as EU governments and the European Parliament negotiate final texts.

"President Trump's behaviour is unacceptable," Bernd Lange, the chair of the European Parliament's international trade committee, told Reuters.

"This latest move demonstrates just how unreliable the US side is. We have already witnessed these arbitrary ​attacks from the US in ​the case of Greenland; this ⁠is no way to treat close partners. Now we can only respond with the utmost clarity and firmness, drawing on the strength of our position," Lange said.

But a Trump administration official, ​asked to explain Trump's move, said: "The EU has not complied with the autos deal after ​eight months."

Shares ⁠of Ford Motor fell 2% after Trump's announcement, while those of Stellantis were down 1.7%. General Motors shares dropped 1.1%.

Ryan Majerus, a former senior US Commerce Department official who is now a partner with King & Spalding, said the president's move also may be ⁠related to ​Trump's frustration that some European countries had baulked at supporting the US-Israeli war against ​Iran.

"This is not going to sit well in the EU, and I'm not sure the administration cares, because they're so incredibly antagonistic toward the EU," Majerus said.