(AFP) -- "Donald Trump's decision not to certify the accord and to demand that Congress strengthen sanctions is, to my eyes, a double fault," Hollande told a conference in Seoul.

The former leader's first speech on international affairs since leaving the Elysee in May touched on global issues including climate change, economic protectionism and populist politics -- and laid into the "confusion" appearing to emanate from the White House.

Trump has said the agreement was letting Iran off the hook but left it up to the US Congress to decide whether to reimpose sanctions.

The former French leader said the US president's actions showed a "deep misunderstanding of the negotiation's purpose", which was to "stop Iran from obtaining weapons, and not to make it change its politics".

He also accused Trump of "damaging the credibility of any future negotiations with North Korea" with Washington's about-turns, a concern shared by European Union ministers.

"It has to be shown that agreements will be kept to in the long term," Hollande said.

The EU said Monday it would send its chief diplomat Federica Mogherini to Washington next month to fight for the nuclear deal.

Hollande said the world "has not been this polarised, in different ways, since 1945".

"And the role of the United States serves to further complicate the situation, especially if confusion reigns at its top."

In the face of nuclear proliferation, the world needed "certainty and stability", he added. "The worst option is unpredictability, which can lead to irrationality."

(Photo: AFP)