The US and Iran will hold talks next week on Tehran's nuclear ambitions, Donald Trump said, as he hailed a swift end to the war with Israel.

The US president said his decision to join Israel's attacks by targeting Iranian nuclear sites with huge bunker-busting bombs had ended the conflict, calling it "a victory for everybody".

"It was very severe. It was obliteration," he said, shrugging off an initial assessment by the US Defense Intelligence Agency that Iran's path to building a nuclear weapon may have been set back only by months.

Speaking in The Hague where he attended a NATO summit on Wednesday, he said he did not see Iran getting involved again in developing nuclear weapons. Tehran has always denied decades of accusations by Western leaders that it is seeking nuclear arms.

"We're going to talk to them next week, with Iran. We may sign an agreement. I don't know. To me, I don't think it's that necessary," Mr Trump said.

Anxious Iranians and Israelis sought to resume normal life after the most intense confrontation ever between the two foes.

Israel's nuclear agency assessed the strikes had "set back Iran's ability to develop nuclear weapons by many years". The White House also circulated the Israeli assessment, although Mr Trump said he was not relying on Israeli intelligence.

He said he was confident Tehran would pursue a diplomatic path towards reconciliation.

"I'll tell you, the last thing they want to do is enrich anything right now. They want to recover," he said.

He added that if Iran tried to rebuild its nuclear programme, the US "won't let that happen".

"Number one, militarily we won't," he said, adding that he thought "we'll end up having something of a relationship with Iran" to resolve the issue.

The head of the UN's nuclear watchdog, Rafael Grossi, dismissed what he called the "hourglass approach" of assessing damage to Iran's nuclear programme in terms of months needed to rebuild as besides the point for an issue that needed a long-term solution.

"In any case, the technological knowledge is there and the industrial capacity is there. That, no one can deny. So we need to work together with them," he said.

His priority was returning international inspectors to Iranian nuclear sites, which he said was the only way to find out precisely what state they were in.