Iran has increased its reserves of enriched uranium by 50%, the IAEA said. Nuclear Weapon News

As negotiations with the United States continue, UN nuclear regulators warn that Tehran may be close to weapons-rich uranium.

The UN nuclear regulator said Iran has increased its highly abundant stocks by 50% over the past three months.

The International Atomic Energy Agency (IAEA) report on Saturday was a nuclear deal negotiation between the United States and Iran, and Tehran insisted that its nuclear program was for peaceful purposes only.

Iran has accumulated 408.6 kg (900.8 pounds) of uranium enrichment as high as 60% as of May 17, the only non-nuclear weapon state for the UN agency – its inventory has increased by nearly 50% to 133.8 kg since its last report in February.

A wide range of confidential reports seen by several news organizations say Iran conducted a secret nuclear activity at three locations that long been investigating materials announced to the IAEA, calling it a “serious concern” and warned Tehran to change its curriculum.

However, Iranian Foreign Minister Abbas Araghchi reiterated the country's long-term position, saying Tehran believes nuclear weapons are “unacceptable”.

“If the problem is nuclear weapons, yes, we also think this type of weapon is unacceptable,” Araghchi, chief negotiator for Iran’s nuclear negotiations with the United States, said in a televised speech. “We agree with them on this issue.”

“Both sides build leverage”

However, the report was requested by the IAEA's 35 national council in November and would allow the U.S., UK, France and Germany to declare Iran breach of its non-proliferation obligations.

On Friday, U.S. President Donald Trump said Iran “cannot possess nuclear weapons.”

Trump added: “They don't want to be blown up. They would rather make a deal.

In 2015, Iran reached an agreement with the United Kingdom, the United States, Germany, France, Russia, China and the European Union, known as the Joint Comprehensive Action Plan. It involves some sanctions on Tehran in exchange for restrictions on its nuclear development plans.

But in 2018, then-U.S. President Trump unilaterally resigned from the agreement and reimposed severe sanctions. Tehran then rebuilt its stockpile of enriched uranium.

In December, the International Atomic Energy Agency said Iran quickly enriched uranium to 60% purity, getting closer to the 90% threshold required for weapon-grade materials.

Western countries say this dense richness should not be part of civilian nuclear program, but Iran insists it will not develop weapons.

Hamed Mousavi, a professor of political science at the University of Tehran, told Al Jazeera that the IAEA's findings could indicate that Iran may have a negotiation tool during nuclear negotiations with the United States.

“I think both sides are trying to establish leverage on the other side. From an Iranian perspective, advances in the nuclear program will allow them to leverage in negotiations with the Americans,” he said.

On the other hand, the United States may threaten more sanctions and could also forward Iran cases to the UN Security Council to violate the 2006 non-proliferation agreement, he said. However, he added that Iran has not made a “political decision” to create the bomb.

“From Iran's perspective, up to 60% of (uranium) is a leverage to raise sanctions on Americans,” Mousavi said.