VIENNA >> The U.N. atomic watchdog said today Iran continues to stay within the limitations set by the nuclear deal reached in 2015 with major powers, though its stockpiles of low-enriched uranium and heavy water are growing.

In a confidential quarterly report distributed to member states and seen by The Associated Press, the International Atomic Energy Agency said Iran has stayed within key limitations set in the so-called Joint Comprehensive Plan of Action, or JCPOA.

The deal is meant to keep Tehran from building atomic weapons in exchange for economic incentives. It has been complicated by the unilateral withdrawal of the United States last year and Washington’s increased sanctions, which has been taking a toll on the Iranian economy.

That has left the other signatories — Germany, Britain, France, Russia and China — struggling to come up with enough incentives to keep Iran in the deal.

Earlier this month, Iran announced that if a way couldn’t be found within 60 days to shield it from U.S. sanctions targeting its economy and oil industry, it would increase its enrichment of uranium beyond the purity allowed under the JCPOA. And about a week ago, Iran said it had increased its uranium-enrichment production capacity, though only of the lower-enriched uranium permitted by the agreement.

In its first quarterly report since those announcements, however, the Vienna-based IAEA found Iran continued to be in compliance with the JCPOA and also said its inspectors had been given unfettered access to Iranian nuclear facilities.

“Timely and proactive cooperation by Iran in providing such access facilitates implementation of the additional protocol and enhances confidence,” the report stated, referring to the procedure detailing safeguards and tools for verification.

A senior diplomat, who was speaking on condition of anonymity because he wasn’t officially allowed to discuss the report, said Iran does have the capacity to quadruple uranium enrichment as it recently threatened, but that inspectors would have to wait until the next report to determine whether they had actually set that increase in motion.

“They have the flexibility, they can increase and they can reduce, and they can do a number of things,” the diplomat said. “The capacity is always there, and we do verify this at a technical level, we are fully monitoring that.”

The IAEA said Iran’s heavy water stockpile was 125.2 metric tons (138 U.S. tons) as of May 26, up from 124.8 tons in February but below the 130 ton limit. Its stock of low-enriched uranium was 174.1 kilograms (383.8 pounds) as of May 20, up from 163.8 kilograms in February; the limit is 202.8 kilograms.

It added that Iran had not enriched any uranium above the level allowed by the JCPOA.

“All centrifuges and associated infrastructure in storage have remained under continuous agency monitoring,” the IAEA said.