French President Emmanuel Macron, wrapping up his three-day state visit with an address to a joint session of the US Congress, cautioned against abandoning the Iran nuclear deal without a substantial alternative.
"We signed it at the initiative of the United States… That is why we cannot say we should get rid of it," he said.
In a wide-ranging speech punctuated with standing ovations, Mr Macron hailed the "unbreakable bonds" of the special relationship between France and the United States. But he also had clear differences with his host.
Mr Macron has been trying to coax US President Donald Trump not to abandon the 2015 Joint Comprehensive Plan of Action (JCPOA), as the deal with Iran is called. "France will not leave the JCPOA," Mr Macron said.
But he emphasised: "Our objective is clear - Iran shall never possess any nuclear weapons. Not now, not in five years, not in 10 years, never."
"It is true to say that this agreement may not address all concerns," he said. "But we should not abandon it without having something more substantial instead."
German Chancellor Angela Merkel will visit the White House tomorrow with a similar message.
Mr Macron said a key focus was developing a more comprehensive deal that, among other things, contained Iran's influence in the Middle East and imposed a moratorium on ballistic missiles.
Iranian President Hassan Rouhani, however, has rejected the idea of rewriting the nuclear deal. "We have an agreement called the JCPOA," he said in a fiery speech. "It will either last or not. If the JCPOA stays, it stays in full."
Mr Macron also spoke on the threats of climate change and "commercial wars". Mr Trump withdrew the US from the Paris Agreement to curb global warming soon after taking office, and has vowed to use tariffs to fight for fair and reciprocal trade.
"We require to offer our children a planet that is still habitable in 25 years," Mr Macron said.
"Some people think that securing current industries and their jobs is more urgent... but we must find a transition to a low-carbon economy. What is the meaning of our lives if we destroy the planet, what is the meaning of our decisions if we reduce the opportunities of our children and our grandchildren?
"By polluting the oceans, not mitigating CO2 emissions and destroying our biodiversity, we are killing our planet. Let's face it, there is no planet B."
"On this issue, it may happen we have disagreements between the United States and France, but that for me is a short-term disagreement. We will have to face the same realities as citizens of the same planet. We have to work together with business leaders and local communities… to make our planet great again and create new jobs and new opportunities while safeguarding our earth," he said.
"And I'm sure that one day the United States will come back and join the Paris Agreement."
In another message aimed at his host, Mr Macron also spoke out in support of the World Trade Organisation, saying: "We need free and fair trade for sure. A commercial war is not consistent with our mission, our history, our commitments for global security. At the end of the day, it will destroy jobs, increase prices, and the middle class will have to pay for it."