The head of the U.N. nuclear agency said Monday that Iran is complying with obligations limiting uranium enrichment, but two diplomats say the agency has warned Tehran that unless it slows the process it could soon bust through its cap on material that could be used to make a bomb.

A nuclear deal between Iran and six world powers stipulates that Iran can possess only low-enriched uranium — which is not suitable for weapons — and no more than 300 kilograms (660 pounds) at any time. That’s far less than would be needed to make a nuclear weapon, even if it were further enriched to weapons-grade levels.

But even a slight violation of Iran’s enrichment commitments would be politically volatile at a time when the deal is on shaky ground. The incoming U.S. administration wants the agreement renegotiated, and many American lawmakers oppose it. Iran says it won’t renegotiate the deal, and accuses the United States of reneging on commitments to lift sanctions.

The two senior diplomats, whose main focus is Iran’s nuclear program, spoke only on condition of anonymity because they are not authorized to discuss confidential messages between the U.N’s International Atomic Energy Agency and Iran.

Iran insists it is not interested in nuclear arms. Its president, Hassan Rouhani, said after weekend talks with IAEA chief Yukiya Amano that his country would abide by the deal if other nations do as well.

An IAEA statement said Amano “stressed the vital importance of full implementation by Iran of its nuclear-related commitments.” Asked whether he had concerns about Iran’s stockpile of enriched uranium, he told reporters that Tehran is within the limits — “for now.”

While Iran has generally kept its obligations since the deal was implemented in January, it has twice exceeded the limit on stockpiles of heavy water, which cools reactors that produce large amounts of plutonium.

(AP)