"Terrorism is spreading and the possibility of using nuclear material cannot be excluded," International Atomic Energy Agency (IAEA) chief Yukiya Amano told AFP in an interview late yesterday.
"Member states need to have sustained interest in strengthening nuclear security," he said. "The countries which do not recognise the danger of nuclear terrorism is the biggest problem."
Amano's comments came before a summit of around 50 leaders in Washington on March 31-April 1 on ensuring that nuclear material in the world's roughly 1,000 atomic facilities are secured.
The material, filmed by a camera in bushes outside the official's home, was reportedly found at the property of Mohamed Bakkali, incarcerated in Belgium for his links to the Paris attackers.
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One Belgian newspaper reported that the device was collected by none other than brothers Ibrahim and Khalid El Bakraoui -- two of the suicide bombers in this week's Brussels attacks.
The Washington summit is part of a process begun by US President Barack Obama in a speech in Prague in 2009 and follows similar gatherings in Seoul in 2012 and The Hague in 2014.
But according to the International Panel on Fissile Materials, enough plutonium and highly enriched uranium still exist to make 20,000 weapons of the magnitude that levelled Hiroshima in 1945.
A grapefruit-sized amount of plutonium can be fashioned into a nuclear weapon, and according to Amano it is "not impossible" that extremists could manage to make a "primitive" device -- if they got hold of the material.
"It is now an old technology and nowadays terrorists have the means, the knowledge and the information," he said.
This is a device using conventional explosives to disperse radioactive material other than uranium or plutonium.
Such material can be found in small quantities in universities, hospitals and other facilities the world over, often with little security.