In unusually strong comments, the German head of state said that just as there was no going back from Russia's 2022 full-scale invasion of Ukraine, "there will be no going back to before January 20, 2025", when US President Donald Trump entered the White House for a second time.

"The rift is too deep and the trust in American power politics has been lost, not only among our allies but... worldwide," he said at an event to mark the 75th anniversary of the German foreign ministry.

Although Steinmeier's role is largely ceremonial, his words carry weight in Germany, which has not officially condemned the war against Iran.

Steinmeier, a former foreign minister, said: "Our foreign policy does not become any more convincing simply because we do not call a breach of international law a breach of international law."

He stressed that the US-Israel war on Iran was, "in my view, in breach of international law".

"There is little doubt that, in any case, the justification of an imminent attack on the US does not hold water," he added.

Germany's head of government, Chancellor Friedrich Merz, has harshly criticised Iran's leadership and backed several key US-Israeli war goals but also stated that, had Berlin been consulted in advance, it "would have advised against" the war.

Merz has repeatedly said Germany shares "the objective that Iran should no longer pose a threat in future", while also making clear Germany would not enter the conflict.

Steinmeier called the military campaign "a politically disastrous mistake" and "a truly avoidable, unnecessary war".

"Realism means we must be pragmatic in our dealings with this US administration and focus on our core interests," he said.

"But realism also means we must not compromise our own principles.

"The US government has a different world view to ours, one that shows no regard for established rules, partnership or hard-won trust.

"We cannot change that. We must deal with it. But this is my conviction: we have no reason to align ourselves with this world view."