Iran has accelerated its enrichment of uranium to near weapons-grade, the U.N. atomic watchdog said in a report on Tuesday seen by Reuters, a move raising tensions with the West as both sides seek to resume talks on reviving Tehran's nuclear deal.

Iran increased the purity to which it is refining uranium to 60% fissile purity from 20% in April in response to an explosion and power cut at its Natanz site that damaged output at the main underground enrichment plant there.

Iran has blamed the attack on Israel. Weapons-grade is around 90% purity.

In May the International Atomic Energy Agency reported that Iran was using one cascade, or cluster, of advanced centrifuges to enrich to up to 60% at its above-ground pilot enrichment plant at Natanz. The IAEA informed member states on Tuesday that Iran was now using a second cascade for that purpose, too.

Where before Iran was using 164 IR-6 centrifuges to enrich up to 60% it was now using that cascade and another of 153 IR-4 machines for that work, the IAEA report said.

The move is the latest of many by Iran breaching the restrictions imposed by the 2015 nuclear deal, which capped the purity to which Tehran can refine uranium at 3.67%. The United States and its European allies have warned such moves threaten talks on reviving the deal, which are currently suspended.

On Monday the IAEA said Iran had made progress in its work on enriched uranium metal despite objections by Western powers that there is no credible civilian use for such work. Uranium metal can be used to make the core of a nuclear bomb but Iran says its aims are peaceful and it is developing reactor fuel.