The International Atomic Energy Agency document, the ninth since the deal came into force in January 2016, showed Iran complying with the accord's key parameters.

The number of centrifuges to enrich uranium was below the agreed level of 5,060, while Iran's total stockpile of low-enriched uranium "has not exceeded 300 kg", said the report seen by AFP.

Uranium when enriched to high purities can be used in a nuclear weapon. At low purities it can be used for peaceful applications such as power generation -- Iran's stated aim.

The volume of heavy water, a reactor coolant, remained below the agreed maximum of 130 tonnes throughout the past three months.

Iran has inched above that ceiling twice since the accord took effect.

It removed and rendered inoperable the core of the Arak reactor, which could in theory have produced weapons-grade plutonium, before the accord entered into force.

Aside from the relatively minor breach on heavy water, the IAEA reports have consistently shown Iran adhering to the deal in the two years since it took effect.

However, the future of the hard-won agreement between Iran and the five permanent members of the UN Security Council plus Germany is highly uncertain.

Trump in January set a 120-day deadline for US lawmakers and European allies to "fix" his predecessor Barack Obama's main foreign policy achievement or face a US exit.

He is concerned that parts of the deal start to expire from 2026 and that it fails to address Iran's missile programme, its regional activities or its human rights abuses.

A US exit could kill the nuclear deal, which the Islamic republic has refused to re-negotiate.

While Iran has reaped massive economic benefits from the accord, notably by being able to resume oil exports, it is still constrained by US sanctions in other areas.

Russian Foreign Minister Sergei Lavrov has warned Europe signatories against compromising on the deal, saying it would be a "slippery slope in a very dangerous direction".

- Nuclear subs? -

The IAEA report also said that Iran informed it in January by letter of a decision to "construct naval nuclear propulsion in future".

The IAEA has asked Tehran for further details. Press reports in the past have said that Tehran wants to develop nuclear-powered ships and/or submarines.

This has created concern in the past because of the possibility that Iran might use highly enriched uranium to power such vessels.

However a senior diplomat at IAEA headquarters said that low-enriched uranium could be used instead and that Iran's plans appeared vague for now.

"Everything in the letter only refers to the future. The indirect indication is that (actual designs) don't exist," the diplomat said.

He suggested that the announcement could also be "rhetoric" aimed at the Trump administration.