‘Dirty bombs will be enough to [drive[ any big city in the world into panic,’ Mr Amano said. ‘And the psychological, economic and political implications would be enormous.’

This is thought to be well within the capabilities of extremists, and ISIS has already used chemical weapons, according to CIA director John Brennan.

Probes into the Brussels attacks this week claimed that jihadis may have been plotting to steal nuclear material to create a radioactive bomb.

Highlighting the risks, Belgian police investigating the November 13 Paris terror attacks found 10 hours of video following a senior Belgian nuclear official.