Iran has not responded to the U.N. atomic watchdog on extending their monitoring agreement that expired overnight, the agency said on Friday, calling for an "immediate" answer on the issue that threatens to derail wider talks on the Iran nuclear deal.

The agreement continues the International Atomic Energy Agency's collection of data on some of Tehran's activities, cushioning the blow of Iran's decision in February to reduce cooperation with the agency.

"An immediate response from Iran is needed in this regard," the IAEA said in a statement summarising a report by its chief Rafael Grossi to its 35-nation Board of Governors that was also seen by Reuters.

The agreement stipulates the IAEA cannot access the data collected until a later date, provided the agreement holds. Grossi wrote to Iran last week "to understand Iran's position regarding the possible continued collection, recording and retention of data", the report said.

As of Friday, Iran had not replied or indicated whether it intends to maintain the current arrangement, it said.

"The Director General stresses the vital importance of continuing the Agency's necessary verification and monitoring activities in Iran, including the uninterrupted collection and storage of data by its monitoring and surveillance equipment," it added.

Iran and the United States have been holding indirect talks on reviving the 2015 nuclear deal between Iran and major powers that imposed restrictions on Tehran's nuclear programme in exchange for a lifting of international sanctions.