UN Secretary General Antonio Guterres has urged Donald Trump not to walk away from an international deal designed to prevent Iran acquiring nuclear weapons.
Speaking to the BBC, Mr Guterres said there was a real risk of war if the 2015 agreement was not preserved.
Mr Trump has been a strong critic of the accord, in which Iran agreed to limit its nuclear programme in return for the lifting of sanctions.
The US president has until 12 May to decide whether to stick with the deal.
Mr Guterres told the BBC that the Iran agreement was an “important diplomatic victory” and should be maintained.
“We should not scrap it unless we have a good alternative,” he said, adding: “We face dangerous times.”
It comes just days after Israel revealed “secret nuclear files” accusing Iran of having covertly pursued nuclear weapons.
US Secretary of State Mike Pompeo said the files provided proof that the Obama-era nuclear deal was “built on lies”.
European allies France, the UK and Germany meanwhile have agreed that pursuing the current nuclear deal with Iran is the best way to stop it developing nuclear weapons.
What is the Iran deal?
In 2015 Tehran signed a deal with the US, China, Russia, Germany, France and Britain agreeing to limit its nuclear activities in return for the lifting of crippling economic sanctions.
Under the deal, officially known as the Joint Comprehensive Plan of Action (JCPOA), Iran is committed to slashing the number of its centrifuges, which are machines used to enrich uranium.
It is also meant to cut its stockpile of enriched uranium drastically and not enrich remaining uranium to the level needed to produce nuclear weapons.
The number of centrifuges installed at Iran’s Natanz and Fordo sites was cut drastically soon after the deal while tonnes of low-enriched uranium were shipped to Russia.
Furthermore, monitors from the IAEA have been able to carry out snap inspections at Iranian nuclear sites.
On Monday, Israeli Prime Minister Benjamin Netanyahu revealed what he said were pages of material that proved Iran had covertly pursued nuclear weapons.
Speaking in English from Israel’s defence ministry in Tel Aviv, Mr Netanyahu showed off what he said were “exact copies” of documents obtained by Israeli intelligence from a secret storage facility in Tehran.