The UN nuclear watchdog and Iran have agreed to extend an understanding to monitor Tehran's activities by one month, the agency said Monday, while talks in Vienna try to save the 2015 nuclear deal.

"The equipment and the verification and the monitoring activities that we agreed will continue as they are now for one month expiring on June 24th, 2021," International Atomic Energy Agency (IAEA) director general Rafael Grossi told a news conference.

Iran in late February limited the IAEA's access to nuclear sites it has been monitoring as part of the 2015 landmark deal.

An agreement, reached on February 21 for a duration of three months, allowed some inspections to continue.

Grossi said that besides extending that understanding, Tehran had also agreed that information collected so far by agency equipment in Iran would not be erased.

He said the outcome of this "long discussion" was "important" but the situation was "not ideal".

"We should all be reminded that the temporary understanding is a sort of stop-gap measure. It is to avoid flying completely blind," he said.

The 2015 accord, which had Iran curtail its nuclear programme in return for sanctions relief, started to unravel in 2018 when the US withdrew and reimposed sanctions.

Current talks between world powers are aiming to bring the US back into the deal and lift sanctions in exchange for Iran reversing nuclear activities it stepped up after Washington pulled out.

Iran said Monday that talks in Vienna depend on a "political decision" by the US, after Washington questioned Tehran's readiness to return to compliance with the accord.

US Secretary of State Antony Blinken had said it remains unclear whether Iran is "ready and willing" to take the necessary steps to return to compliance with the multi-nation nuclear agreement.