CIA director John Brennan has warned that ISIS fighters have already used chemical weapons and have the capacity to make small quantities of deadly chlorine and mustard gas.

The terrorist organisation was already believed to have smuggled weapons of mass destruction into Europe, according to a UN report.

According to Brennan: 'We have a number of instances where ISIL has used chemical munitions on the battlefield.'

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CIA director John Brennan has admitted ISIS has the ability to manufacture chlorine and mustard gas

Brennan, right, said US intelligence agencies were trying to identify the ISIS stockpiles in Iraq and Syria

Director of National Intelligence, James Clapper, pictured, said ISIS has used poison gas in Iraq and Syria

Brennan made the admission during a full interview with CBS show '60 Minutes' which will be aired on Sunday.

He warned: 'There are reports that ISIS has access to chemical precursors and munitions that they can use.'

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

He said: '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.'

When asked if there were 'American assets on the ground' searching for possible chemical weapons caches or labs, Brennan replied: 'US 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.'

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

Clapper, who is director of national intelligence, told the committee: 'ISIL has also used toxic chemicals in Iraq and Syria, including the blister agent sulfur mustard.'

Bashar al-Assad's regime has also been accused of dropping chemical weapons on civilians

Hundreds of people required treatment, including these children, following a suspected poison gas attack on the rebel-held Damascus suburb of Saqba in August 2013

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.

President Bashar al-Assad's regime and rebel forces have accused each other of using chemical agents in the nearly five-year war that has killed more than 250,000 people.

After an August 2013 sarin attack outside Damascus that much of the international community blamed on Assad's government, the regime agreed to turn over its chemical arsenal.

The Organization for the Prohibition of Chemical Weapons (OPCW) -- which oversaw the dangerous removal and elimination of Syria's avowed stockpile -- now says that declared arsenal has been completely destroyed.

But the global arms watchdog has still warned of the continued use of mustard, sarin and chlorine gas in the conflict, without blaming the regime, the rebels or ISIS for use of the weapons, which are banned under international law.

Last year, officials in the autonomous Iraqi region of Kurdistan said blood tests had shown that ISIS fighters used mustard agent in an attack on Kurdish peshmerga forces in August.

Thirty-five peshmerga fighters were exposed and some taken abroad for treatment, officials said.

At the time of the attack, The Wall Street Journal cited US officials as saying they believed ISIS had used mustard agent.

Late last year, a report for the European Parliament claimed ISIS had recruited experts with chemistry, physics and computer science degrees to wage war with weapons of mass destruction against the West.

The terror organisation, according to the briefing document, 'may be planning to try to use internationally banned weapons of mass destruction in future attacks'.

The document, which was compiled in the aftermath of the deadly attacks on Paris claimed that ISIS has already smuggled WMD material into Europe.

Experts fear that ISIS will be able to exploit a failure of EU governments to share information on possible terrorists.

Already, British police forces have been conducting exercises on how to deal with various types of terrorist attack. But the EU report claims that government should 'consider publicly addressing the possibility of terrorist attack using chemical, biological, radiological or even nuclear materials'.

The report, ISIL/Da'esh and 'non-conventional' weapons of terror warns: 'At present, European citizens are not seriously contemplating the possibility that extremist groups might use chemical, biological, radiological or nuclear (CBRN) materials during attacks in Europe. Under these circumstances, the impact of such an attack, should it occur, would be even more destabilising.'

Rob Wainwright, head of Europol said after the attacks on Paris: 'We are dealing with a very serious, well-resourced, determined international terrorist organisation that is now active on the streets of Europe.

'This represents the most serious terrorist threat faced in Europe for 10 years.'

Mr Wainwright warned that ISIS had serious capabilities in terms of resources and manpower.'

Nomi Bar-Yaacov, Associate Fellow in Chatham House's International Security Department said: 'There is a very real risk of ISIS using unconventional weapons in Europe and beyond.'

Wolfgang Rudischhauser, Director of the Weapons of Mass Destruction Non-Proliferation Centre at NATO said: 'ISIS actually has already acquired the knowledge, and in some cases the human expertise, that would allow it to use CBRN materials as weapons of terror.'

The report claims 'ISIL/Da'esh has recruited and continues to recruit hundreds of foreign fighters, including some with degrees in physics, chemistry and computer science, who experts believe have the ability to manufacture lethal weapons from raw substances.'

EU governments have been warned to watch out for 'other radicalised individuals, who have access to, or work in, sensitive areas'.

Intelligence services have also been warned to screen returning Jihadi fighters for 'specialist CBRN knowledge'.

The shocking study claims that 150 cases of nuclear or radiological trafficking are reported annually.

Worse still: 'CBRN substances have been carried undetected into the European Union.