US intelligence says Iran not building nuclear bomb as Tehran reveals new underground base

Assessment by US spy agencies says Iran's research is designed for diplomatic 'leverage'

Amir Ali Hajizadeh, right, commander of Iran's Islamic Revolutionary Guards Corps aerospace force, and Maj Gen Mohammad Hossein Bagheri, chief of staff of Iran's Armed Forces, tour a recently completed underground missile base. Photo: IRGCShow less

Iran is not seeking a nuclear weapon, despite UN assessments that Tehran has rapidly increased enrichment of uranium to levels sufficient to build several weapons.

That is the view of the US intelligence community in its Annual Threat Assessment, released on March 25.

“We continue to assess Iran is not building a nuclear weapon and that [supreme leader Ali] Khamenei has not reauthorised the nuclear weapons programme he suspended in 2003, though pressure has probably built on him to do so,” the report said.

“In the past year, there has been an erosion of a decades-long taboo on discussing nuclear weapons in public that has emboldened nuclear weapons advocates within Iran’s decision-making apparatus. Khamenei remains the final decision maker over Iran’s nuclear programme,” the document said.

US intelligence community view

The 31-page report represents the joint view of up to 18 US intelligence agencies, from the CIA – the US foreign intelligence service, to the Pentagon’s Defence Intelligence Agency, the National Security Agency, which monitors communications, and the National Reconnaissance Office, which operates spy satellites.

It could surprise observers listening to President Donald Trump, who has warned Iran to stop its nuclear research programme or face military consequences.

Israel has long threatened to bomb sites serving Iran's nuclear programme, which it views as developing a bomb, and has sought US assistance for what experts expect would be a days-long campaign of air strikes.

The report was published as Iran revealed more of its vast underground military infrastructure on Tuesday, some dedicated to protecting nuclear facilities from air attack, and some bases dedicated to housing drones and missiles.

Iranian state media showed a video of a subterranean “missile city” being toured by Maj Gen Mohammad Hossein Bagheri, chief of staff of Iran’s Armed Forces, and Amir Ali Hajizadeh, who commands the aerospace forces of the Islamic Revolutionary Guard Corps.

Iran has shown several similar underground bases in the past, housing drones, attack boats and even fighter aircraft including US-made F-4 Phantoms supplied to the US-backed regime of Shah Mohammad Reza Pahlavi in the 1970s.

Warhead challenge

The US assessment makes no estimate of how close Iran might be to a nuclear bomb, if it desired to develop one, only noting that Mr Khamenei is the final decision maker.

Iran's supreme leader Ayatollah Ali Khamenei delivers his annual speech for Nowruz, the Persian new year, on March 21, 2025. Iran's Supreme Leader Office / EPA

Clement Therme, a non-Resident Fellow at the International Institute for Iranian Studies, agrees with the US assessment.

“Since the beginning of the Iranian nuclear file on the international scene in 2002, Iran’s nuclear programme has been primarily about leverage – using its capabilities as a bargaining chip to extract concessions from the West while stopping short of weaponisation,” he said.

“Iran has a history of using nuclear advancements as a pressure tool in negotiations, particularly after the US withdrawal from the JCPOA (2015 Joint Comprehensive Plan of Action) in 2018.

“At the same time, Iran has accumulated significant technical know-how and stockpiles of highly enriched uranium, which shorten its theoretical breakout time. In other words, Iran is a threshold nuclear state: the decision to weaponise or not weaponise is not a technical one but a political one.”

The UN’s nuclear watchdog, the International Atomic Energy Agency, said Iran could have material for several bombs if it chose, based on its calculations of Tehran's current stockpile of uranium enriched above 60 per cent. Nuclear bombs require uranium enriched to 90 per cent, but experts say the leap from 60 to 90 per cent enrichment is a minor technicality.

However, nuclear weapons are particularly heavy and it is not clear whether Iran could build a bomb small enough to be carried by a missile, a process known as miniaturisation that is regarded as a tough engineering challenge.

The reliability of an Iranian weapon – whether it would definitely explode if used – is also the subject of scientific speculation.

Most public knowledge about Iran’s weapons programme was released in 2018, when Israeli agents – or people acting on behalf of the Mossad intelligence agency – broke into a warehouse outside Tehran and stole a trove of documents from the nuclear archive.

The documents, analysed and verified by the UN and other experts, detail Iran’s efforts at Parchin, a huge military centre associated with missile research, in particular efforts to compress nuclear material with high implosive force, using shaped explosive charges.

A satellite image of the Parchin Military Complex in March 2021. Imagery courtesy Maxar Technologies via Google Earth, Infographics courtesy of The Intel Lab

According to the Institute for Science and International Security, the work was conducted in the early 2000s and may have been halted in 2003. The institute said that a document leaked in 2009 suggests that research to develop an “initiator” for a nuclear explosion may have continued.

Since then, experts have only been able to guess as to Iran’s true nuclear ambitions and whether large facilities, many of them inspected by the UN under the 2015 nuclear deal, could be hiding the full extent of its nuclear project.

The institute detailed the complexity of the nuclear detonator research conducted at Parchin in 2019.

“The timing of the explosion and resulting shock waves would need to be near perfect in order to create enough fusion to result in a spurt of neutrons, both in a reliable manner and at exactly the right instant. The experiment itself is very difficult to do,” the institute said.

“Until now, for the sake of the survival of the Iranian political system, the decision of the supreme leader has been not to weaponise Iranian nuclear activities while at the same time increasing its comprehensive nuclear activities and research programme to retain the option to seek nuclear weapons if the political calculus at the top-level decision making process of the Iranian state,” Mr Therme says.

In October last year, sources told US news site Axios that a round of Israeli strikes on Iran had hit facilities for “active” nuclear weapon research, without elaborating.

Despite the assessment that Iran is not pursuing a nuclear bomb, the US intelligence report says “Tehran will try to leverage its robust missile capability and expanded nuclear programme” to pressure the US, Israel and other opponents.