A former scientist for the Syrian chemical weapons programme said the regime of President Bashar al-Assad has enough of the nerve agent sarin to "eradicate the whole of Damascus, Homs, Hama, and Aleppo".



Speaking to Al Jazeera on condition of anonymity after he fled from Syria, the chemist added that the regime is not likely to unleash its chemical stockpiles unless it “no longer cares about the world knowing".



"If the regime is to fire a Scud-B with a chemical warhead filled with sarin, the missile would create a chemical cloud in the atmosphere that is 3km long and 500m wide, which could be fatal to all people under it," the chemist said.



He claims that the regime has only used sarin nerve gas in small quantities to halt rebel advances in four towns in the suburbs of Damascus, in Aleppo’s Sheikh Maksoud district, in Idlib's Saraqeb town and in Homs' al-Khalidiyeh district.



"The intention was to incapacitate rebels and force them out of strategic areas, while keeping the deaths among their ranks limited," the chemist said, who added that he was speaking out "to dispel the myths on chemical weapons in Syria".



Al Jazeera was able to verify his former position at the chemistry institute of the Centre for Scientific Studies and Research (CSSR), Syria’s main agency for the development and enhancement of weaponry. It has been reported that a CSSR site in the Damascus suburb of Jamraya was targeted twice earlier this year by Israeli airstrikes.

Syria's stockpile



The Syrian government has managed to keep information about its chemical weapons largely beyond the reach of outsiders, and to keep its scientists under heavy surveillance, even keeping some under 24-hour guard.



The exiled chemist says Syria’s stockpile comprises 700 tonnes of sarin agent, at least 3,000 aerial bombs that could be filled with chemical agents and more than 100 chemical warheads for Scud missiles.



Consistent with other intelligence reports, the chemist said that Assad’s chemical weapons arsenal also contains mustard gas and what experts describe as the deadliest of all nerve agents, VX.

"It was our dogma that we were creating the equivalent of Israel’s nuclear weapons" - Former chemist at the Centre for Scientific Studies and Research



Some Western intelligence agencies believe that Syria also has access to tabun nerve agent, but the chemist said these reports are untrue.



The regime and rebels have accused each other of using chemical weapons on several occasions, and the issue has come to dominate recent debate about the two-year-long conflict.



While the US and Britain say they have "credible evidence" that chemical weapons have been used in Syria, and Turkey said its hospitals treated patients exposed to chemical attack, a UN human rights inquiry said it had "no conclusive findings on use of chemical weapons".



Weaponisation of sarin



The chemist said he fled the country before December 23, 2012, when the first claims emerged about the regime’s use of chemical weapons in the neighbourhood of Khaldiyeh, in the city of Homs. The neighbourhood is strategic because it divides Sunnis and largely pro-government Alawites.



A diluted mix of sarin and isopropyl alcohol was likely used in December 2012, according to the scientist, but he cast doubt on the claims of the regime and rebels that chemical weapons were used in Khan al-Assal in Aleppo on March 19.



Sarin is a colourless and odorless liquid. "When medics report [a] very disgusting smell, the way they did in Khan al-Assal, it is obvious it’s not coming from chemical weapons," the chemist said. "The fact that patients only suffered from suffocation and no other symptoms further confirms that it was not sarin."



View Alleged chemical weapons attacks in a larger map

The chemist said what was likely fired was military-grade tear gas, used as a substitute for chemical agents. The chemist explained that during the two-year conflict, the regime has experimented with mixing different gases - like sarin and tear gas - in order to create a mélange of symptoms that would make the cause hard to identify.

"When opposition activists report different kinds of symptoms resulting from the different gases, it becomes hard to believe them. Some opposition fighters report a burning sensation in the eyes, raising the question as to whether this was tear gas or nerve gas," the chemist said.



Salman al-Sheikh, the director of the Brookings Doha Center, said that mixing different gases is a way for the regime to test the "red line" set down by US President Barack Obama, which - if crossed by the use of chemical weapons - could require firm action by the international community. But once the regime found no serious international response, it carried on with the use of chemical arms in different strategic areas, he said.



Supervisor 'forcibly held'



The exiled chemist said plans to use chemical agents against rebel forces were formed in December 2012, just after the disappearance of his former supervisor, a CSSR scientist. The chemist believes his supervisor is currently being forcibly held by the regime to find solutions to stabilise sarin in small munitions like cannon shells.



Assad’s military is believed to have long-range weapons systems capable of delivering chemical weapons via warheads on ballistic missiles, or through bombs dropped by aircraft.



Members of the supervisor’s family and two of his colleagues at the CSSR told Al Jazeera that he was kidnapped in December, but they refused to elaborate on who might have abducted him or why, citing security concerns. Al Jazeera is withholding the name of the supervisor for security reasons.



The exiled scientist estimates the number of CSSR employees at around 9,000 people, with up to 6,000 working in rocket development and around 300 in chemical weapon development. None of the staff are authorised to speak to the media or reveal the nature of their work. Their movements are heavily scrutinised by the Syrian regime.



“Syrian researchers who work with chemical weapons are not known to people at the street level, nor to the ministries, nor to the general army,” the chemist said.

Army loyalty



Scientists in the chemistry institute work in close collaboration with two secret army units, 451 and 452, which handle chemical weapons and have the responsibility for securing stockpiles.



General Zaher al-Saket, the former head of the chemical warfare administration in the Syrian Army’s 5th Division, who defected last month, told Al Jazeera he was one of the candidates set to be promoted to Unit 451. But the regime wanted to make sure all those handling chemical weapons were loyal to the regime, so "they chose Colonel Mohammad Ali Wannous, because he was an Alawite", Saket said.



It is not known exactly when chemical weapons production in Syria began. The chemist said that all infrastructure and equipment to produce the nerve agent sarin was provided to Syria by what was then West Germany. As for VX, the chemist said that Syria in the 1990s used the expertise of Armenian specialists trained in the Soviet Union before its collapse.



Allegations of foreign assistance to Syria’s chemical weaponisation are difficult to assess due to the heavy veil of secrecy surrounding the programme.



“The project was developed with national hands”, the chemist said, adding that he did not see evidence of cooperation from Iran or North Korea.



The scientist said the regime had convinced him that the weapons he was working on were for self-defence against Israel. "It was our dogma that we were creating the equivalent of Israel’s nuclear weapons," the chemist said. "Never were we told that the weapons could be used inside the country."

Follow Basma Atassi on twitter: @Basma_