CIA director John Brennan
CIA director John BrennanReuters

CIA director John Brennan is warning that  Islamic State (ISIS) fighters have used chemical weapons and have the capability to make small quantities of chlorine and mustard gas, AFP reports.

"We have a number of instances where ISIL has used chemical munitions on the battlefield," Brennan was quotes as having told CBS News, which released excerpts of an interview with him that will air in full on the "60 Minutes" news program this coming Sunday.

ISIL is an alternative acronym for ISIS.

The network added that Brennan told "60 Minutes" the CIA believes that ISIS has the ability to make small amounts of mustard or chlorine gas for weapons.

"There are reports that ISIS has access to chemical precursors and munitions that they can use," he was quoted as having said.

Brennan also warned of the possibility that ISIS could seek to export the weapons to the West for financial gain.

"I think there's always the potential for that. This is why it's so important to cut off the various transportation routes and smuggling routes that they have used," he said.

When asked if there were "American assets on the ground" searching for possible chemical weapons caches or labs, Brennan replied, "U.S. intelligence is actively involved in being a part of the efforts to destroy ISIL and to get as much insight into what they have on the ground inside of Syria and Iraq."

Brennan’s comments follow several reports which said that ISIS had used mustard agent in both Syria and Iraq.

In September, American intelligence officials said they “knew” ISIS was using chemical attacks in both countries, adding the jihadists used such weaponry “on at least four separate occasions on both sides of the border.”

The question has been asked how ISIS managed to get its hands on chemical weapons in the first place. One possible answer is that in June 2014, ISIS seized a weapons complex thought to have held hundreds of tons of lethal sarin and mustard gasses: the al-Muthanna complex, located 60 miles north of Baghdad, which was a central base of former Iraqi dictator Saddam Hussein's chemical weapons program. 

There has also been some speculation that ISIS got its hands on chemical stockpiles that belonged to former Libyan dictator Muammar Qaddafi.

A former intelligence official of Qaddafi’s recently said in a television interview that ISIS and other terrorist groups had gotten hold of the chemical weapons that had remained in Libya and smuggled them somehow to Syria.

The release of the excerpts of Brennan's interview comes two days after similar comments from spy chief James Clapper before a congressional committee.

"ISIL has also used toxic chemicals in Iraq and Syria, including the blister agent sulfur mustard," Clapper, the director of national intelligence, told lawmakers on Tuesday, according to AFP.

He said it was the first time an extremist group had produced and used a chemical warfare agent in an attack since Japan's Aum Supreme Truth cult carried out a deadly sarin attack during rush hour in the Tokyo subway in 1995.