Donald Trump attacked Germany's Friedrich Merz after the chancellor criticized the US handling of its war on Iran.
Merz earlier this week said American negotiators were being "humiliated" by the Iranian leadership as the conflict, which has triggered global energy turmoil, approaches its third month.
"The Chancellor of Germany, Friedrich Merz, thinks it's OK for Iran to have a Nuclear Weapon," Trump wrote in a post on Truth SocialBloomberg Terminal Tuesday. "He doesn't know what he's talking about! If Iran had a Nuclear Weapon, the whole World would be held hostage."
The retort was delivered a day and a half after Merz weighed in with an unusually candid assessment of Trump's negotiating strategy. Speaking to a group of students at a school in western Germany on Monday, the chancellor said he didn't grasp the US exit strategy -- and lauded Tehran's negotiators for moving "very skilfully -- or indeed very skilfully not negotiating."
An "entire nation is being humiliated by the Iranian leadership," Merz said.
The comments didn't sit well with the US leader, who argued that his push on Iran's nuclear program was something "other Nations, or Presidents, should have done long ago."
"No wonder Germany is doing so poorly, both Economically, and otherwise!"
A spokesman for Merz declined to comment. Germany has consistently demanded that Iran curtail its nuclear enrichment program, adhere to verification standards and abandon any pursuit of an atomic weapon.
Germany joined the five permanent members of the United Nations Security Council -- the US, UK, France, Russia and China -- to negotiate the Joint Comprehensive Plan of Action in 2015, in which Iran agreed limit its program in exchange for sanctions relief. Trump jettisoned the JCPOA three years later.
The chancellor's comments underscore frustration among European leaders and a reassessment of their relations with Trump. A tendency to smooth ties by currying favor has given way to a more sober perspective of a US president who has repeatedly called into question NATO, bolstered European far-right forces and threatened to seize Greenland, a territory of Denmark.