After months of smiles and sympathetic overtures, North Korea has once again bared its teeth, casting doubt on the planned summit with Donald Trump and personally lambasting John Bolton, the US president’s national security adviser.

But for analysts, Pyongyang’s volte face serves as a timely wake-up call for Washington that dismantling the reclusive regime’s nuclear programme is likely to be a hard-fought, bitterly contested and potentially futile endeavour.

The challenges are myriad and set over several stages. First, both sides need to agree on what constitutes denuclearisation. Then a deal must be negotiated that provides North Korea with sufficient security guarantees. Finally, the deal must be enforced, a process that is practically impossible given a dearth of intelligence in the west about Pyongyang’s nuclear programme.