US President Donald Trump (R) and German Chancellor Friedrich Merz at the White House

US President Donald Trump has lashed out at Friedrich Merz after the German chancellor criticized the American aggression against Iran for lacking a clear exit strategy and said Tehran was "humiliating" Washington with its negotiating tactics.

In a post on his Truth Social platform on Tuesday, Trump said Merz "doesn`t know what he`s talking about!"

Earlier, Merz had described the aggression as "ill-considered."

"The problem with conflicts like this is always you don`t just have to get in - you have to get out again. We saw that very painfully in Afghanistan for 20 years. We saw it in Iraq," he had added.

Merz had also said Washington was being "humiliated" by Islamic Republic`s negotiating tactics after Tehran refused to rejoin negotiations with Washington, despite the latter`s repeated announcements of its intentions to send over delegates for continuation of the talks.

Trump, however, tried to defend the aggression, saying, "I am doing something with Iran, right now, that other Nations, or Presidents, should have done long ago."

His remarks echoed his repeated attacks on the US`s NATO allies over their refusal to directly join the aggression, which saw some members even close their airspaces to flights contributing to attacks targeting the Islamic Republic.

Trump went on to extend his criticism of Merz to the way he was running his country.

"No wonder Germany is doing so poorly, both Economically, and otherwise!"

His comments marked a clear departure from how he would describe Germany during Merz`s last visit to the White House, during which Trump described the European country as "a respected" one and said he had "a very good relationship with the country - in particular now, with this leader."