The United States told Iran on Tuesday that it must let the UN atomic agency continue to monitor its activities, as laid out in an agreement that has been extended until June 24, or put wider talks on reviving the Iran nuclear deal at risk.

The International Atomic Energy Agency and Iran reached a three-month agreement in February cushioning the blow of Tehran's decision to reduce its cooperation with the agency by ending extra monitoring measures introduced by the 2015 deal.

Under that new side agreement, which on May 24 was extended by a month, data continues to be collected in a black-box-type arrangement, with the IAEA only able to access it at a later date. It is unclear whether the agreement will be extended again; the IAEA has said such negotiations are getting harder.

"We strongly encourage Iran to avoid any action that would prevent the collection of or IAEA access to the information necessary for it to quickly re-establish ... continuity of knowledge," a US statement to a meeting of the International Atomic Energy Agency's 35-nation Board of Governors said.

"Such action would, at a minimum, seriously complicate ongoing efforts to reach an understanding on how Iran can return to compliance with its JCPOA commitments in return for a similar US resumption," it added, referring to the 2015 deal by its full name, the Joint Comprehensive Plan of Action.

Indirect US-Iran talks on reviving the deal are due to resume in Vienna this week. The data covered by the separate IAEA-Iran agreement includes real-time uranium enrichment levels as well as whether centrifuges, machines that enrich uranium, remained in storage and the production of centrifuge parts.