Iran's stockpile of enriched uranium is more than five times the limit fixed under a landmark 2015 deal with world powers, the UN nuclear watchdog said on Tuesday.

An International Atomic Energy Agency (IAEA) report said as of February 19, 2020, the Iranian stockpile stood at 1,510 kilogrammes, as opposed to the 300kg limit set under the agreement.

Some analysts consider this level could provide sufficient material to produce a nuclear weapon. However, it would still need several more steps, including further enrichment, to make it suitable for use in an atomic bomb.

"Iran has not provided access to the agency to two locations ... and not engaged in substantive discussions to clarify agency questions related to possible undeclared nuclear material and nuclear-related activities," a second IAEA report said.

"The director general calls on Iran to immediately cooperate fully with the agency, including by providing prompt access to the locations specified," said the confidential report seen by news agencies.

It added Iran informed the IAEA it "will not recognise any allegation on past activities and does not consider itself obliged to respond to such allegations".

Hanging by a thread 

The nuclear deal with Iran was signed in 2015 by the United States, Germany, France, the United Kingdom, China and Russia.

The historic accord has been hanging by a thread since the US withdrew from it in May 2018 and imposed stinging sanctions on Iran, in particular targeting its vital oil sector.

The latest IAEA reports come just days after a meeting in Vienna of the remaining parties to the deal, which ended without a clear plan to keep the accord alive.

The agreement promised Iran an easing of punishing economic sanctions in return for its scaling back its nuclear programme.

Tehran has been progressively reducing its commitment to the accord in retaliation for the US move.