The International Atomic Energy Agency's second quarterly assessment since the accord came into force on January 16 showed that Iran was meeting its main commitments.
The report showed that Iran "has not pursued the construction of the existing Arak heavy water research reactor" and has "not enriched uranium" above low levels.
Iran's stockpile of low-enriched uranium, material which can be used for peaceful purposes but when further processed for a nuclear weapon, has not risen about the agreed level of 300 kilos (660 pounds).
The level of so-called heavy water has not exceeded the permitted level of 130 tonnes, as it did briefly during the previous reporting period. Verification by the IAEA has continued as agreed.
The IAEA added that "all stored centrifuges and associated infrastructure have remained in storage under continuous Agency monitoring" and no enriched uranium has been accumulated through research and development activities.
The steps taken by Iran under the 2015 deal extend to at least a year the length of time Tehran would need to make one nuclear bomb's worth of fissile material -- up from a few months before the accord.
Signup to our newsletter and follow us on Facebook and Twitter!
They included slashing by two-thirds its uranium centrifuges, cutting its stockpile of uranium -- several tonnes before the deal, enough for several bombs -- and removing the core of the Arak reactor which could have given Iran weapons-grade plutonium.
Centrifuges are machines that "enrich" uranium by increasing the proportion of a fissile isotope, rendering it suitable for other purposes.
Throughout the 12-year standoff that preceded the deal, Iran always denied wanting nuclear weapons, saying its activities were exclusively for peaceful purposes such as power generation.
In return for the scaling down of its nuclear activities, painful UN and Western sanctions were lifted on the Islamic republic, including on its lifeblood oil exports.
Iran however has complained that major powers have been slow to implement their side of the bargain, with badly needed foreign investment into the country proving slower than hoped.
The United States has maintained its sanctions targeting Tehran's alleged sponsorship of armed movements in the Middle East and its ballistic missile programme.
European banks, which often have subsidiaries on US soil, have therefore been slow to resume business with Iran, fearing prosecution in the United States.
Iranian Foreign Minister Mohammad Javad Zarif on May 21 called on Washington to take "more serious and concrete actions" to alleviate the situation.