Observers say North Korea could be creating a secret new generation of nuclear weapons.

Activity based around a remote factory near the capital Pyongyang is thought to be connected to the manufacture of weapons-grade uranium.

The fact that Kim Jong-un has never been pictured visiting the Kangson facility is highly unusual

The Kangson facility has been known to US Intelligence since 2007, but now the International Atomic Energy Agency (IAEA) appears to have confirmed that the site is nuclear in nature and currently active.

Rafael Mariano Grossi, director general of the IAEA, said: “We are trying to fine-tune the analysis on Kangson.

“In the beginning we were a bit more prudent, but with further analysis we can see that this is a relevant place where activity is taking place.”

Satellite images are suggestive of major nuclear development

US-based magazine, The Diplomat, described in 2018 the mounting circumstantial evidence that points to Kangson being a secret nuclear site.

At its heart is a 51,000 square-foot hall which is believed to house the centrifuge cascades producing highly-enriched uranium.

Satellite photos reveal that snow never gathers on its roof, even when nearby rooftops are covered, suggesting that it creates heat all year round.

Plus it’s less than a mile away from a major motorway – a lifeline for a facility that generates a lot of waste and needs regular resupply – and it's just two and a half miles from Chamjin Missile Factory.

The Kangson facility started to take shape in the early 2000s and is thought to have been enriching weapons-grade uranium for as long as 17 years

Kangson also stands out because it is the only major facility in the area that neither Kim Jong-un nor his predecessor, Kim Jong-il, have ever been shown visiting in North Korean propaganda.

It’s even surrounded by a 3,200ft long perimeter wall – suggesting a high-security area.

A number of support buildings at the site are thought to be home to scientists, engineers and other staff.

A US intelligence source told The Diplomat that Kangson’s capacity could be twice that of the Yongbyon site, another nuclear facility that has been openly acknowledged by the Kim regime.

In April 2018, Kim Jong-un promised he was suspending long-range nuclear missile tests and shutting test sites

While a different US government source estimated in 2017 that, between the two sites, North Korea had enough fissile material for 12 new nuclear weapons a year.

Since then, a suspected third site has been detected by US military intelligence.

Mr Grossi said that identifying Kangson as a nuclear site was important in case North Korea decided to allow IAEA inspectors to return to the country.

Despite the denuclearisation pledge, the rogue state has not stopped its nuclear activities

He said: “For me this is important because, when we return to the DPRK – and I hope this will indeed be the case – we will have in front of us a much wider set of facilities and places to visit.

“So it’s good that we start to get a feel of what could be taking place in different parts of the country.”

Mr Grossi also confirmed that up-to-date satellite imagery was helping them keep track of the site.

"It’s all of that," he said.

“It’s more information but it’s also perhaps more inspectors, more equipment and that takes time.

"And we are at a time of enormous budgetary restrictions so we are basically relying on voluntary contributions from some countries that are willing to help us beef up our operation.

“Because when something happens then we will be requested to be there immediately and if we are not prepared it would be quite bad.”