US President

Without revealing his decision, Trump told journalists "I have decided" ahead of an October 15 deadline to re-up the agreement. "I’ll let you know what the decision is," he said.

Trump has already reapproved sanctions relief for Tehran and is not expected to declare Iran in non-compliance with an Obama-era agreement to scale back uranium enrichment.

But he could still refuse to recertify the agreement by the October deadline, a decision that is still fiercely contested inside Trump's adminstration and is likely to be the subject of numerous discussions in the next month.

While the White House wants to confront Iran over its ballistic missile program and support for proscribed groups across the Middle East, there is no consensus on whether the US should back away from the nuclear deal.

Doing so could provoke an international crisis, infuriating allies in Europe and setting up confrontation with powerful Iranian forces and proxies from Yemen to the Strait of Hormuz.