On Monday, Mr Merz claimed the US "obviously went into this war without any strategy". He said during a discussion with students at a high school in Marsberg in the Sauerland region: "Especially since the Iranians obviously negotiate very skillfully - or do not negotiate very skillfully. An entire nation is being humiliated by the Iranian leadership." During the discussion, the Germany's Chancellor also said: "Because the Iranians are obviously stronger than previously thought, and the Americans clearly lack a truly convincing strategy in the negotiations." However, the criticism appears to have infuriated Mr Trump, who has responded in furious fashion in a post on Truth Social.

He wrote: "The Chancellor of Germany, Friedrich Merz, thinks it’s OK for Iran to have a Nuclear Weapon. He doesn’t know what he’s talking about!

"If Iran had a Nuclear Weapon, the whole World would be held hostage.

"I am doing something with Iran, right now, that other Nations, or Presidents, should have done long ago.

"No wonder Germany is doing so poorly, both Economically, and otherwise! President DONALD J. TRUMP."

Tensions between Mr Trump and NATO have skyrocketed since the beginning for the Iran war exactly two monts ago.

Earlier this month, the US president even warned he was ready to reconsider America's membership of the alliance after the conflict.

He said: "Oh yes, I would say [it’s] beyond reconsideration. I was never swayed by NATO. I always knew they were a paper tiger, and Putin knows that too, by the way."

Mr Trump also rebuked Sir Keir Starmer for refusing to get involved in the US-Israeli war against Iran, and suggested the Royal Navy was not ready.

He then added that he had set "very disappointing" NATO allies a deadline to send warships to the Strait of Hormuz, something that was considered an “ultimatum” by European diplomats.