Iraqi and American intelligence officials say 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.

The American officials tell The Associated Press they do not believe IS group 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. The officials spoke on condition of anonymity to discuss the intelligence on the IS program.

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