The International Atomic Energy Agency is policing the deal, which lifted sanctions against Tehran in exchange for restrictions on Tehran's atomic activities aimed at increasing the time Iran would need to make an atom bomb if it chose to.
Iran has remained within the key limits on its nuclear activities imposed by its 2015 deal with major powers despite growing pressure from newly reimposed US sanctions, a report by the UN nuclear watchdog showed on Friday.
Iran has stayed within caps on the level to which it can enrich uranium, as well as its stock of enriched uranium, the IAEA said in a confidential quarterly report sent to its member states and obtained by Reuters.
"Not much has changed..., a continuing reporting of the implementation (by Iran)," a senior diplomat said on condition of anonymity, summarising the report.
The IAEA also repeated its usual statement that it carried out so-called complementary access inspections - which are often at short notice - at all locations in Iran that it needed to visit.
President Donald Trump pulled the United States out of the Iran nuclear deal last May, reimposing US sanctions on Iran's economy and lifeblood oil industry that were lifted under the 2015 agreement.
European powers that signed the deal - France, Britain and Germany - have sought to cushion the blow to Iran of those sanctions.
They are setting up a new channel for non-dollar trade with Iran but diplomats say it will not be able to handle the big transactions Iran says it needs to keep the deal afloat.
Setting up that channel, however, has angered Washington for undermining its effort to choke Iran's economy in response to Tehran's ballistic missile programme and its influence on the wars in Syria and Yemen.
The US Vice President Mike Pence last week called on those European powers to follow Washington in pulling out of the agreement despite their long-held position that the deal is worth keeping as long as Iran sticks to it.
Iran has long said that it wants nuclear power only for purposes of civilian energy.
Iran's stock of heavy water, a substance used as a moderator in some nuclear reactors, stayed within the limit set by the deal and Tehran continued to ship some of it out of the country, with 1 tonne having been exported during the quarter.
The senior official said it was sold to an unspecified IAEA member state.