But al-Zamili, citing intelligence reports he has access to, told the AP that the group has managed to attract chemical experts from abroad as well as Iraqi experts, including ones who once worked for Saddam Hussein's now-dissolved Military Industrialization Authority. The foreigners include experts from Chechnya and southeast Asia, the Iraqi intelligence officials said.
ISIS recently moved its research labs, experts and materials from Iraq to "secured locations" inside Syria, al-Zamili added - apparently out of concern of an eventual assault on Mosul, Iraq's second largest city, captured by ISIS in the summer of 2014.
"Daesh is working very seriously to reach production of chemical weapons, particularly nerve gas," al-Zamili said, using an Arabic acronym for the group. "That would threaten not just Iraq but the whole world."
Still, U.S. intelligence officials say they don't believe ISIS has the technological capability to produce nerve gas or biological agents, and that the militants were more likely to harm themselves trying to make them. A European official privy to intelligence on the extemist group's programs agreed, saying so far even IS production of mustard gas was in small quantities and of low quality.
Retired Lt. Gen. Richard Zahner, who was the top American military intelligence officer in Iraq in 2005 and 2006 and went on to lead the National Security Agency's electronic spying arm, noted that al-Qaida tried for two decades to develop chemical weapons and didn't succeed, showing the technical and scientific difficulties.
However, he said, U.S. intelligence agencies have consistently underestimated the Islamic State group, which has shown itself to be more capable and innovative than al Qaeda and has greater financial resources. Given that and its inheritance of Saddam-era experts, he said, it could realistically reach a "limited" program for battlefield uses.
"Even a few competent scientists and engineers, given the right motivation and a few material resources, can produce hazardous industrial and weapons-specific chemicals in limited quantities," Zahner said.
Developing chemical weapons has been an ambition of the group - and various other jihadi movements - for years.
In a 2013 report on ISIS' weapons procurement efforts, a senior deputy of ISIS leader Abu Bakr al-Baghdadi wrote of "significant progress" toward producing chemical weapons, according to two senior officials who had access to the document after it was obtained by Iraqi intelligence.
In it, the deputy, Sameer al-Khalifawy, wrote that chemical weapons would ensure "swift victory" and "terrorize our enemies." But, he added, what was needed was "to secure a safe environment to carry out experiments."
Al-Khalifawy was killed by rebels in Syria in early 2014, just months before IS overran Mosul and much of northern and western Iraq, linking that territory to the stretches of northern and eastern Syria it controlled and declaring itself a "caliphate."
In May 2013, Iraqi security forces, acting on a tip from the Americans, raided a secret chemical weapons research lab in Baghdad's Sunni-majority district of al-Doura, the Iraqi intelligence officials said. Security forces arrested two militants running the lab, Kefah Ibrahim al-Jabouri, who held a master's degree in chemistry, and Adel Mahmoud al-Abadi, who has a bachelor's degree in physics and worked at Saddam's Military Industrialization Authority before it was disbanded in 2003.
The Iraqi officials said the two men were working with al-Baghdadi, citing ISIS correspondence they seized from al-Jabouri. Other international officials disputed this, however, saying the men were not connected with the group.
Iraqi officials complained of lack of cooperation from neighboring Syria.
They cited the case of a veteran Iraqi jihadist and weapons expert, Ziad Tareq Ahmed, who fled to Syria after Iraqi security agents raided his Baghdad home in 2010 and arrested members of his cell. The agents found large amounts of material that could be used for making mustard gas.
Ahmed, who has a master's degree in chemistry and has worked with several Islamic militant groups without formally joining any, was arrested by the Syrians last year. The Syrian government allowed Iraqi officals to interrogate him in prison but refused to hand him over. Then last month, they released him, two Iraqi intelligence officials said.
"This is a very grave development," said one of the officials, who heads one of Iraq's top counterterrorism agencies. "His release adds significantly to our concerns."