* Iran still in breach of two central limits of nuclear deal
* Stock of enriched uranium growing, enrichment level stable
* Iran says it will breach deal's limits one by one
* U.S. has offered talks, Iran wants sanctions relief first
* IAEA report says Iranian cooperation could be better (Adds detail)
By Francois Murphy
VIENNA, Aug 30 (Reuters) - Iran has gone further in breaching its nuclear deal with world powers, increasing its stock of enriched uranium and refining it to a greater purity than allowed, the U.N. atomic agency report said on Friday.
The quarterly report from the International Atomic Energy Agency, which is policing the 2015 deal, confirms Iran is progressively backing out of the deal in retaliation for Washington's withdrawal form the accord and renewal of sanctions that have hit Iranian oil sales.
Iran has said it will breach the deal's limits on its nuclear activities one by one, ratcheting up pressure on parties who still hope to save it.
U.S. President Donald Trump has offered to hold talks with Iran on a broader deal but Tehran says first it must get relief from U.S. sanctions.
In July, the IAEA said Iran exceeded both a 202.8-kg limit on its enriched uranium stock and its 3.67% cap on the fissile purity to which it is allowed to refine uranium. In a verbal update on July 10, the IAEA said Iran was enriching uranium to 4.5% purity and had stockpiled 213.5 kg of enriched uranium.
Friday's quarterly report to member states obtained by Reuters said Iran has accumulated 241.6 kg of enriched uranium and is enriching at around the same level as before, up to 4.5%.
Iran's enriched uranium stock is still a fraction of the tonnes it possessed before the deal. Its enrichment level is also well short of the 20% it reached before the deal and the roughly 90% that is considered weapons-grade.
Its breaches have therefore not yet made much difference to the time it would need to obtain enough fissile material for a nuclear bomb if it sought one. The deal - which set nuclear restrictions in exchange for sanctions relief - extended that time to roughly a year from a few months.
Iran has threatened to take further steps by Sept. 6, such as enriching to 20% or restarting mothballed centrifuges, machines that enrich uranium.
The report also hinted at less than ideal cooperation from Iran, saying: "Ongoing interactions between the Agency and Iran ... require full and timely cooperation by Iran. The Agency continues to pursue this objective with Iran."
A senior diplomat added, however, that Iran had not changed its level of cooperation and IAEA inspectors were able to visit all the locations in the country they needed to.
The message was an encouragement to do more to help answer outstanding questions rather than provide access, he added, without elaborating. Diplomats have often said Iran has dragged its feet while stopping short of crossing the IAEA's red lines. (Reporting by Francois Murphy Editing by Mark Heinrich and Andrew Heavens)