The United States called on Iran on Wednesday to dilute all of the uranium it has enriched to up to 60% purity, close to the weapons-grade level of roughly 90%, in a statement denouncing many of Tehran's recent nuclear moves.

The International Atomic Energy Agency said in a confidential report to member states last week that Iran's stock of uranium enriched to up to 60% had fallen slightly in the past quarter as it had diluted, or "downblended," more of its most highly enriched material than it had produced.

Iran still has enough of that material, if enriched further, to fuel two nuclear weapons by a theoretical IAEA definition, and enough for more bombs at lower enrichment levels, the report seen by Reuters showed.

"Iran should downblend all, not just some, of its 60% stockpile, and stop all production of uranium enriched to 60% entirely," the United States said in a statement on Iran to a quarterly meeting of the 35-nation IAEA Board of Governors.

It is not clear why Iran downblended the material. It denies seeking nuclear weapons and says it has the right to enrich to high levels for civil purposes. Western powers say there is no credible civil justification for enriching to such high levels.

"We continue to have serious concerns related to the stockpile of highly enriched uranium that Iran continues to maintain," the U.S. statement said.

"No other country today is producing uranium enriched to 60% for the purpose Iran claims and Iran's actions are counter to the behavior of all other non-nuclear weapons states party to the NPT (Non-Proliferation Treaty)," it added.

The United States also condemned various moves by Iran, many of which the IAEA has also criticized, such as barring some of the IAEA's most experienced and expert inspectors last year.