VIENNA — Iran has started the process of enriching uranium to 60% fissile purity at its above-ground Pilot Fuel Enrichment Plant at Natanz, the UN nuclear watchdog said on Saturday, confirming earlier statements by Iranian officials, Reuters reported.

"The Agency today verified that Iran had begun the production of UF6 enriched up to 60% U-235 by feeding UF6 enriched up to 5% U-235 simultaneously into two cascades of IR-4 centrifuges and IR-6 centrifuges at the Natanz Pilot Fuel Enrichment Plant," the International Atomic Energy Agency (IAEA) said in a statement.

UF6 is uranium hexafluoride, the form in which uranium is fed into centrifuges for enrichment.

The move has complicated talks aimed at reviving Iran's nuclear deal with major powers as it is a big step towards producing weapons-grade uranium. Iran had previously only reached 20% purity, and that was already a breach of the deal, which says Iran can only enrich to 3.67%.

Iran made the step up to 60% in response to an explosion that damaged equipment at the larger, underground Fuel Enrichment Plant at Natanz. Tehran has blamed Israel and named a man wanted in connection with the blast.

Earlier Saturday, Japan expressed serious concern over Iran's announcement of producing enriched Uranium, at 60%, a high level that puts it near the capacity to produce (nuclear) weapons, under the positively ongoing dialogue over the Iranian nuclear file, among the states concerned.

In a statement, the spokesman of the Japanese Minister of Foreign Affairs called Iran to commit to the joint comprehensive working plan, to refrain from taking any measurement that may demise the accord and work in a constructive manner aiming at solving the dispute, through dialogue.

Japan reasserted that it will continue the diplomatic efforts to mitigate the tensions and for stable situation in the region of the Middle East and to consolidate the international system of non-nuclear proliferation, in coordination with the pertinent countries and international organizations, including the International Atomic Energy Agency (IAEA). — SPA