The US and Iran will hold high-level talks on Tehran’s nuclear programme for the first time in 10 years this weekend.

Whether officials from either side will actually meet in person in Oman is currently unclear, with Donald Trump promising “direct” discussions, while the Iranians insist on a mediated process.

What is clear, however, is that the threat of a nuclear-armed Iran is significantly greater than it was a decade ago, thanks in part to fears of a “crude” weapon that could be rushed online within months.

The Obama administration struck a multinational deal in 2015 to limit Iran’s nuclear production in return for sanctions relief, an agreement Mr Trump unilaterally pulled America out of in his first term.

Back then, the calculus was all about keeping Iran at least 12 months away from producing enough weapons-grade material to build a bomb.

Now, after years of uranium enrichment in Iran following the US withdrawal, intelligence officials from the US, Israel and elsewhere believe Iran could manage that within a week.

That is not the same as having a viable weapon.

For that – in simple terms – engineers would need to shape the uranium into a metal core, assemble it around a neutron source, then overlay this with a sophisticated high-explosive detonator.

From Iran’s point of view, that would ideally be followed by a process of “cold” tests to check the detonation device, potentially followed by an underground test of a real bomb to assess the yield.

They would then need to match the warhead to a ballistic missile.