Isil terrorists are planning to use drones to spray nuclear material over Western cities in a horrific “dirty bomb” attack, David Cameron has warned.

World leaders are concerned that jihadists want to buy basic drones that are widely available online to transport radioactive material into the heart of major cities in a strike that could kill thousands.

The Prime Minister warned that the dangers of Islamic State of Iraq and the Levant (Isil) getting hold of nuclear material was “only too real”.

Mr Cameron on Friday met world leaders, including the presidents of America, France and China, to plan how they would react to such an attack.

Footage has reportedly emerged showing Isil using drones and the threat was deemed so serious that – in a highly unusual move – world leaders were asked to take part in war games to plan how they would respond.

One scenario, mapped out by US officials and presented at the special Nuclear Security Summit session in Washington DC, spelt out the danger in remarkable detail.

It imagined radioactive material had been taken from a medical facility by “insiders” and sold to extremists through the internet’s secretive “dark web”.