Speaking at the close of a G7 summit in France, Trump also said maritime traffic in the Strait of Hormuz had risen sharply since the truce was announced three days ago and expressed hope it could mark the start of a wider peace across the Middle East.
"So the one thing I didn't want to see is, I didn't want to see economic catastrophe. If you kept this going, that could have happened," Trump said.
He thanked Chinese President Xi Jinping and Russian President Vladimir Putin for being "neutral" during the conflict, saying they had not thwarted his efforts to curb Iran's nuclear ambitions.
Oil prices fell again on Wednesday on prospects for the reopening of the Strait of Hormuz, with Brent crude futures below $US80 - their lowest level since the opening salvos of the US-Iran conflict.
But they later regained more than one per cent after Trump said he could resume the war if he was unsatisfied with Iran.
Speaking to reporters, a senior US official read out the text of the signed memorandum of understanding with Iran but said the parties could still walk away until a binding deal is reached.
The 14-point draft, which had already circulated widely before its contents were published, extends a ceasefire announced in April by another 60 days to allow the two sides to negotiate a permanent truce.
The memorandum - expected to be signed at a ceremony in Switzerland on Friday - aims to bring about the "immediate and permanent termination of military operations on all fronts, including in Lebanon," the official said.
Under the terms of the document, neither side would carry out further military operations against the other after the agreement is signed.
The two parties also commit to "respect each other's sovereignty and territorial integrity and to refrain from interfering in each other's internal affairs".
They further agree to begin negotiations aimed at reaching a final agreement within a maximum of 60 days, although that deadline could be extended by mutual consent.
According to the text, the US naval blockade imposed on Iran would be lifted in full within 30 days of the signing of the framework agreement while US military forces in the region would be reduced to their pre-war levels within 30 days of the conclusion of a final agreement.
Commercial vessels would be guaranteed safe and toll-free passage through the Strait of Hormuz for 60 days.
The US official said Iran was expected to work with Oman and other Gulf countries bordering the waterway on a longer-term arrangement to ensure continued free passage.
The US also commits under the framework agreement to work with regional partners on a plan worth at least $US300 billion ($A426 billion) for the reconstruction and economic development of Iran.
Trump on Wednesday gently rebuked Israeli Prime Minister Benjamin Netanyahu over his tactics in Lebanon against Hezbollah.
The two men have repeatedly clashed over Israel's refusal to constrain its pursuit of Hezbollah in Lebanon, where a cessation of hostilities is a key Iranian demand.
"Netanyahu happens to be a good man, gets a little excited sometimes," Trump told reporters.
"We have a little dispute over Lebanon. I say you can do a little softer touch, Bibi," he said, using Netanyahu's nickname.
"You don't have to knock down a building every time somebody walks into it that's from Hezbollah."
Lebanese media reported Israeli air strikes and artillery fire in several southern towns throughout Wednesday.
Lebanese security sources said Hezbollah had also launched two drone attacks on Israeli forces in the south.
Israeli authorities later said five of their soldiers had been injured in two Hezbollah drone attacks in southern Lebanon.
with DPA
