ISIS creating chemical weapons cell in new de facto capital, US official says

• The cell is comprised of chemical weapons specialists from Iraq and Syria
• The new unit is being set up in an ISIS-controlled area in Syria within the Euphrates River Valley

US intelligence believes ISIS is bringing together all of its experts on chemical weapons from Iraq and Syria into a new "chemical weapons cell," according to a US official.

The cell is comprised of chemical weapons specialists from Iraq and Syria who have not previously worked together, the official added. The new unit is being set up in an ISIS-controlled area in Syria within the Euphrates River Valley, between Mayadin, Syria and the town of al Qaim, just across the Iraqi border.

That location has sparked a good deal of interest on the part of US military intelligence. One US defense official told CNN that "thousands" of ISIS operatives and sympathizers may be in the area and that ISIS leader Abu Bakr al Baghdadi could also be in hiding somewhere nearby. The area is now considered the "de facto" capital of ISIS, with Raqqa under such military pressure from the coalition and local forces, the official said.Coalition officials still stress that given its size and status, the capture of Raqqa is still considered to be an important military objective.

It is assessed that ISIS is consolidating its chemical weapons capabilities in order to boost its ability to defend its remaining strongholds.

That stretch has become increasingly important to ISIS, particularly since the US-backed Syrian Democratic Forces have pushed toward Raqqa, the terror group's one-time unofficial capital.

US defense officials have said that they have observed ISIS officials increasingly abandoning Raqqa for towns and cities further south along the Euphrates River, such as Mayadin and Deir-e-Zor.

"We know they have been moving a lot of their leadership out of Raqqa and we suspect much of their technical expertise and planning as well," US Maj. Adrian Rankine-Galloway, a Pentagon spokesman, told CNN.

While not confirming reports of the consolidation of chemical expertise, Col. Ryan Dillon, a spokesman for the US-led military coalition, told CNN that "we have seen ISIS use low-grade chemical agents in the past. We know ISIS is willing to use chemical weapons. This is not something we want to see them get good at."

There has been a significant uptick in low-grade chemical weapons use by ISIS as the terror organization fights to hold on to Mosul.

Military officials told CNN there have been more than 15 chemical weapons attacks since April 14 in or around West Mosul. While there have been no US or coalition casualties, some Iraqi troops have been treated for injuries. Military officials have downplayed the efficacy of ISIS' chemical weapons, saying they have less battlefield effect than conventional explosives.