Islamic State has created a chemical weapons cell in Syria made up of its top specialists from across its new self-titled caliphate, according to US officials.

Having fled both Mosul and Raqqa en masse due to intense military pressure, ISIS terrorists are said to be calling an area it controls within the Euphrates River Valley its de facto capital.

It is here, between Mayadin and the town of al Qaim across the border in Iraq, where the cell is working on its chemical arsenal.

A source in the US defence department said thousands of ISIS terrorists have converged in the area, which is where the group's leader Abu Bakr al-Baghdadi is said to be hiding.

ISIS fighters, pictured, are said to be fleeing Mosul and Raqqa for a stretch of land south of the Euphrates River

Abu Bakr al-Baghdadi, ISIS leader, is said to have made his way to the area and is in hiding

Chemical weapons experts working for ISIS have fled Raqqa and Mosul to set up in Al Qaim

The production faction is made up of chemistry experts from across Iraq and Syria, who have been brought together for the first time, an official told CNN.

With so many of its strongholds under huge pressure from coalition forces, the move is said to be a tactical switch to boost its ability to defend those areas.

Woman beheaded for witchcraft and sorcery ISIS thugs beheaded a woman they claimed was a witch and a sorcerer. The horrifying incident occurred in Deir Ezzor province, Syria. Syrian Observatory for Human Rights said she was butchered in front of children outside the village's postal building. Advertisement

US authorities monitoring the area said they have observed a growing number of ISIS chiefs abandoning Raqqa for the stretch of land south of the Euphrates River.

'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 Major Adrian Rankine-Galloway, a Pentagon spokesman, told CNN.

Colonel Ryan Dillon, a spokesman for the US-led military coalition, told the site that ISIS have used what he called 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,' he said.

The officials' conclusions are backed by the fact there have been more than 15 chemical weapon attacks since April 14 in or around Mosul.

It comes as the terror group killed more than 50 people in an attack on government-held villages in Syria's central Hama province and another incident of a woman getting beheaded for 'witchecraft and sorcery '.