"We are aware that the ISIL has occupied the Al Muthanna complex," State Department spokeswoman Jen Psaki said in a statement. (Agencies)
But she said she didn't think the Islamic State of Iraq and the Levant (ISIL) militants would be able to produce usable chemical weapons there, because any materials remaining are old and unwieldy.
The complex, located just 72 kilometers northwest of Baghdad, began producing mustard gas and other nerve agents, including Sarin, in the early 1980s soon after Hussein took power, according to a CIA factsheet.
The program expanded to its height during the Iran-Iraq war later that decade, and produced 209 and 394 tons of Sarin in 1987 and 1988 respectively.
But the CIA writes that the facility shut down after the first Gulf war, when UN resolutions "proscribed Iraq's ability to produce chemical weapons."
In the early 1990s, the site was used to oversee efforts to destroy Iraq's chemical weapons stockpile.
Psaki said, "We remain concerned about the seizure of any military site by the ISIL."
However, she said, "We do not believe that the complex contains (chemical weapons) materials of military value and it would be very difficult, if not impossible to safely move the materials."
"We are aware that the ISIL has occupied the Al Muthanna complex," State Department spokeswoman Jen Psaki said in a statement.