President Donald Trump will not withdraw from the Iran nuclear deal or reimpose sanctions, but he will say the pact is not in national security interests, US secretary of state Rex Tillerson has said.
Mr Trump is scheduled to give a speech on the nuclear accord, which he has repeatedly denounced as the worst deal in American history.
The plan would allow Mr Trump to keep up his criticism of the deal, while also reassuring US allies that Washington will not walk away from it, at least not immediately.
Mr Tillerson said on Friday that Mr Trump would urge Congress to toughen requirements for Iran to continue to get relief from US sanctions.
In his speech, Mr Trump will notify Congress that he is "decertifying" the deal, known as the Joint Comprehensive Plan of Action, arguing that while Iran may be complying with the letter of the agreement, the accord itself is not sufficient to be in US interests.
In remarks ahead of his address to a group of conservative voters, Mr Trump previewed his position by calling Iran "a terrorist nation like few others" and urged his audience to listen to the speech.
The administration wants Congress also to amend legislation to highlight troubling non-nuclear Iranian behaviour not covered by the deal.
Mr Trump's speech from the White House will outline specific faults he finds in the pact but will also focus on an array of Iran's troubling non-nuclear activities, officials have said.
Those include Tehran's ballistic missile programme, support for Syrian president Bashar Assad, Lebanon's Hezbollah movement and other groups that destabilise the region, including in Yemen.
Under US law, Mr Trump faces a Sunday deadline to notify Congress whether Iran is complying with the 2015 accord that was painstakingly negotiated over 18 months by the Obama administration and determine if it remains a national security priority.
Although Mr Trump will allow that Iran is living up to the letter of the agreement, he will make the case that the deal is fatally flawed and that its non-nuclear behaviour violates the spirit of the regional stability it was intended to encourage, the officials said.
The officials said Mr Trump will not call for a re-imposition of nuclear sanctions on Tehran.
He will instead urge politicians to codify tough new requirements for Tehran to continue to benefit from the sanctions relief that it won in exchange for curbing its atomic programme.
And he will announce his long-anticipated intent to impose sanctions on portions of Iran's Revolutionary Guard Corps by designating them a terrorist organisation under an existing executive order, according to the officials and advisers.