'ISIS 'making, using chem weapons in Syria, Iraq'

There is a growing belief within the US government that the Islamic State militant group is making and using crude chemical weapons in Iraq and Syria, a US official has told the BBC.

The US has identified at least four occasions on both sides of the Iraq-Syria border where ISIS has used mustard agents, the official said.

The US believes the group has a cell dedicated to building these weapons.

"They're using mustard," the individual said of ISIS. "We know they are."

The mustard agent was probably being used in powder form and packed into traditional explosives like mortar rounds, the official said.

When these weapons explode the mustard-laced dust blisters those who are exposed to it.

The official said the intelligence community believes the most plausible explanation is that they are manufacturing it.

"We assess that they have an active chemical weapons little research cell that they're working on to try and get better at it," the official said.

The official said knowledge to make the mustard agent is widely available, and it is not a complex chemical to produce.

And on Thursday, Russia lifted its objections to a UN investigation into chemical attacks in Syria, clearing the way for the probe to begin, diplomats said.

The Russians also wants the investigators to weigh in on the use of chemical weapons in Iraq by Islamic State militants.

Meanwhile, just ahead of the fourteenth anniversary of al Qaeda's 9/11 attacks on the US, the leader of the terrorist group took aim in an angry speech at a mortal enemy -- but not American "crusaders" this time. Rather, the object of his tirade was the leader of ISIS in a declaration of war that will "irreconcilably" divide the two terror groups in a way the US may be able to exploit, experts say.

Ayman al-Zawahiri, who replaced Osama bin Laden as the head of al Qaeda four years ago, in a new audio message accused ISIS top leader Abu Bakr al-Baghdadi of "sedition" and insisted the Iraqi terrorist recluse was not the leader of all Muslims and militant jihad as "caliph" of the Islamic State, as al-Baghdadi had claimed 14 months ago in a Mosul mosque.

ISIS, formerly the al Qaeda branch in Iraq, split from the larger group two years ago. In the tape, al-Zawahiri complained that Baghdadi had ignored Muslims suffering in Gaza and in Pakistan.