Air Component Commander, Air Commodore Justin Reuter, says the militants occupy an area of around two kilometres which is surrounded by cliffs, the Euphrates river, and troops of the Syrian Democratic Forces (SDF), who are looking to recapture the last IS enclave.
The RAF officer says the battlewill be fraught with difficulty.
"It will look very much like a camp but there are tunnels in there," says Air Cdre Reuter.
"There are Daesh fighters mixed in with their families. Women and children. Non-combatants and combatants in a very small area."