Vienna (AFP) - Iran is sticking to the 2015 nuclear deal with major world powers even as tensions rise with US President Donald Trump, a UN atomic watchdog report showed Friday.

Trump has vowed to "dismantle" the "disastrous" deal and has ratcheted up US sanctions, calling for Iran to be isolated and throwing his weight behind Tehran's arch rival Saudi Arabia.

But the new International Atomic Energy Agency report, seen by AFP, showed Iran's nuclear activities remain reduced, making any push to an atomic bomb much harder than before the agreement.

Iran's stock of low-enriched uranium -- used for peaceful purposes, but when further processed for a weapon -- remained below the agreed limit of 300 kilogrammes (661 pounds), the report said.

The quarterly assessment said Iran "has not pursued the construction of the Arak... reactor" -- which could give it weapons-grade plutonium -- and has not enriched uranium above low purity levels.

Iran's stock of heavy water, used as a reactor coolant, was 128.2 tonnes. Iran has previously inched above an agreed ceiling of 130 tonnes a number of times and has shipped the excess abroad.

The agreement between Iran and the United States, Russia, China, France, Britain and Germany was agreed in Vienna in July 2015, after years of negotiations. It came into force in January 2016.

The accord saw Iran substantially reduce its nuclear programme and submit to ultra-close IAEA oversight, making much tougher any "breakout" attempt to make a bomb before the world can react.

In return, UN and Western sanctions related to the nuclear standoff were lifted, in particular on Tehran's oil exports and unlocking billions of dollars in funds frozen oversees.

However, other sanctions related to human rights and Iran's missile activities have remained in place and have even by added to by Trump, frustrating Tehran's efforts to boost trade.

Trump, who on Thursday announced a US withdrawal from the Paris climate agreement, on May 17 renewed a waiver of nuclear-related US sanctions on Iran but he has ordered a review of the main nuclear deal.

Trump in May chose Saudi Arabia for his first foreign trip, announcing $110 billion in arms deals and saying Iran "funds, arms and trains terrorists, militias and other extremist groups... across the region".

US Secretary of State Rex Tillerson has also expressed misgivings about time periods in the Iran deal that mean the Islamic republic can increase its enrichment capacity again from 2026.