Friedrich Merz said the US had been humiliated by Iran, in an overt attack on Donald Trump.

The German chancellor also claimed that Washington “quite obviously went into this war without any strategy”, and said the Iranian leadership had been “negotiating very skilfully”.

Mr Merz said: “The Iranians are clearly stronger than expected and the Americans clearly have no truly convincing strategy in the negotiations either. 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. A whole nation is being humiliated by the Iranian leadership, especially by these so-called Revolutionary Guards.”

Mr Merz reiterated his offer to deploy German minesweepers to help reopen the Strait of Hormuz, but his attack will probably heighten already strained tensions between the US and Europe.

Iran wants to postpone nuclear talks

The reopening of the strait is one of the key stumbling blocks in negotiations to secure a peace deal between Iran and the US.

On Monday, Axios reported that Iran had submitted a new peace proposal to the US, in which it offered to open the key waterway while postponing talks on its nuclear programme.

Iran’s nuclear ambitions have been a major point of contention in negotiations between the two sides, but Tehran hopes the war can end without an agreement on its stockpile of enriched uranium.

The offer, conveyed via Pakistani mediators, reflects deep divisions in Iran over how far it is willing to go in meeting Washington’s demands. It also signals a shift towards securing immediate economic and military relief before tackling longer-term nuclear concessions.

Two US officials confirmed to Axios that the Trump administration had received the proposal, but Washington had made no decision on it. The White House is quoted as saying: “These are sensitive diplomatic discussions and the US will not negotiate through the press.”

Trump: ‘They cannot have a nuclear weapon’

Karoline Leavitt, the White House press secretary, said Donald Trump had discussed the Iranian proposal with his top national security aides on Monday.

On Sunday, Mr Trump insisted that a commitment to non-nuclear proliferation by Iran was a red line. He told Fox News: “They know what has to be in the agreement. It’s very simple: they cannot have a nuclear weapon. Otherwise there’s no reason to meet.”

Abbas Araghchi, the Iranian foreign minister, met Vladimir Putin in Saint Petersburg on Monday and they discussed efforts to end the war.

Mr Araghchi said the Islamic Republic was “stable, solid” during their talks, and claimed: “The world has now realised Iran’s true power.” He added that Russia had stood by Iran and the two countries would continue their “strategic partnership”.