The Islamic State group is aggressively pursuing development of chemical weapons, setting up a branch dedicated to research and experiments with the help of scientists from Iraq, Syria and elsewhere in the region, Iraq and US intelligence officials said.

The American officials said they do not believe IS has the capability to develop sophisticated weapons like nerve gas that are most suited for a terrorist attack. So far the group is believed to have used mustard gas on the battlefield in Iraq and Syria.

In the wake of the Paris attacks claimed by IS, France's prime minister Manuel Valls warned of the potential for an attack by chemical or biological weapons.