President Donald Trump will unveil a more aggressive strategy to check Iran's growing power Friday, but will stop short of withdrawing from a landmark nuclear deal, or declaring the powerful Islamic Revolutionary Guard Corps a terrorist organization.

During a White House speech at 12:45 pm (1645 GMT), Trump is expected to declare the landmark 2015 agreement -- which curbed Iran's nuclear program in return for massive sanctions relief -- is no longer in the US national interest.

Officials say he will not kill the international accord outright, instead "decertifying" the agreement and leaving US lawmakers to decide its fate.

Trump had repeatedly pledged to overturn one of his predecessor Barack Obama's crowning foreign policy achievements, deriding it as "the worst deal" and one agreed to out of "weakness."

The agreement was signed between Iran and six world powers -- Britain, China, France, Germany, Russia and the US -- at talks coordinated by the European Union.

While the deal stalled Iran's nuclear program and thawed relations between Iran and its "Great Satan", opponents say it also prevented efforts to challenge Iranian influence in the Middle East.

Since coming to office, Trump has faced intense lobbying from international allies and his own national security team, who argued the deal should remain in place.

In another partial climbdown, Trump is also expected to levy limited sanctions against the Revolutionary Guards, rather than inviting retaliation by designating it as a terrorist organization.

The outcome "probably reflects more some of the divisions and debates within the administration," said former US Middle East envoy Dennis Ross.

Apart from running swaths of Iran's economy and Iran's ballistic program, the corps is also accused of guiding bellicose proxies from Hezbollah in Lebanon, to the Huthi in Yemen to Shia militia in Iraq and Syria.

- Snap back -

Still, Trump's tough-guy gambit could yet risk undoing years of careful diplomacy and increasing Middle East tensions.

UN nuclear inspectors say Iran is meeting the technical requirements of its side of the bargain, dramatically curtailing its nuclear program in exchange for sanctions relief.

Iranian President Hassan Rouhani lashed out at US counterpart saying he was opposing "the whole world" by trying to abandon a landmark nuclear agreement.

"It will be absolutely clear which is the lawless government. It will be clear which country is respected by the nations of the world and global public opinion," he added.  

And Congress must now decide whether to end the nuclear accord by "snapping back" sanctions, which Iran demanded be lifted in exchange for limiting uranium enrichment. 

Many lawmakers are waiting to see how Trump presents the choice before deciding whether to keep or torpedo the agreement. 

In a statement to AFP, leading Republican Senator Marco Rubio described the accord as "fatally-flawed" and said he was open to legislation that would "substantially improve America's ability to counter Iran's nuclear, terrorism, militancy and regional threats."

- Allies pleading -

Trump has been railing against the Iran deal since before he was elected in November last year.

In office, he has chafed at being required under US law to re-certify Iran's compliance with the accord every 90 days, declaring that Tehran has broken it "in spirit."

Right up until the last minute, America's closest allies have urged him to reconsider.

Secretary of State Rex Tillerson spent much of the week on the telephone, talking through a decision that is deeply unpopular with allies.

After Trump's nationalist UN speech last month, EU foreign policy chief Federica Mogherini warned that the deal "doesn't belong to one country... it belongs to the international community."

US allies have not been convinced by the argument that the deal fell short because it left Iran free to develop ballistic missiles and sponsor proxy militias in its region.

"Mixing everything means risking everything," a French diplomatic source told AFP. "The existential threat is the bomb. The nuclear deal is not meant to solve Lebanon's problems."

Europe fears not only that Iran will resume the quest for the bomb but that the US is relinquishing its leadership role in a stable, rules-based international system.

On Tuesday, British Prime Minister Theresa May called the White House to impress upon it her government's "strong commitment to the deal alongside our European partners." 

In parallel, her foreign minister, Boris Johnson, told his US counterpart Tillerson "that the nuclear deal was an historic achievement."

"It was the culmination of 13 years of painstaking diplomacy and has increased security, both in the region and in the UK," he argued.