Despite an announcement from Iran earlier this month that it no longer considered itself bound by the agreed restrictions on stocks of enriched uranium and heavy water, stocks of both did not exceed the ceilings set in the 2015 agreement, the report said.

As of May 26, Iran had 125.2 metric tonnes of heavy water, an increase of 0.4 tonnes on February but still under the 130-tonne limit.

As of 20 May, Iran had 174.1 kg (383 pounds) of enriched uranium, up from 163.8 kg in February but again within the relevant limit.

The report does say that "technical discussions... are ongoing" with Iran in relation to its installation of up to 33 advanced IR-6 centrifuges, but does not specify the content of these discussions.

Earlier this month Iran announced it was suspending some of its commitments under the 2015 Joint Comprehensive Plan of Action (JCPOA).

The move came a year after US President Donald Trump pulled out of the deal. His administration has also reinforced economic sanctions against the Islamic republic.

As well as no longer respecting the limits on stocks, Iran has also said it will increase production of uranium and heavy water.

The report also confirms Iran has not breached the uranium enrichment level of 3.67 percent specified in the JCPOA.

Since Iran made its announcement earlier this month, there had been "no changes" in the level of co-operation received from Iran, according to a senior Vienna-based diplomat.

The latest report comes amid heightened tensions between Washington and Tehran in recent weeks.

The United States has beefed up its military presence in the Middle East in response to alleged threats from the Islamic republic.