The coalition's strategy for combatting ISIS is taking its toll psychologically
Colonel John Dorrian said ISIS diehards are executing deserters trying to flee the battle for Raqqa in northern Syria.
And the Coalition's policy of deliberately targeting IS or ISIS leaders is leading to "pessimism" even among rank and file fighters.
Col Dorrian, spokesman for the US-led Operation Inherent Resolve, spoke as RAF warplanes and drones kept up raids on IS in and around West Mosul where the battle to retake the terror group's last stronghold in Iraq started on Sunday
In the past few days RAF Tornados and Typhoons have destroyed IS mortar positions, artillery and "choke-points" where truck bombs could have hindered the advance by Iraqi troops.
These are not the actions of an enemy who feel they're winning, and that's because they're not
Colonel John Dorrian
Col Dorrian, speaking in Baghdad, said that meanwhile Syria Democratic Forces are advancing to Raqqa from the north and east.
They have liberated 300 sq miles of territory and more than 100 villages in the past three weeks.
He said: "We're now seeing signs that ISIS fighters, its leaders in Raqqa, are beginning to feel the pressure.
"Specifically, they're becoming increasingly paranoid.
"They've increased population control measures in Raqqa by seeking to remove or destroy televisions, searching houses for mobile phones and satellite dishes in order to maintain control of news and access to information about their losses.
"These are not the actions of an enemy who feel they're winning, and that's because they're not.
"We're seeing reflections of pessimism among mid-level commanders and this world view is spreading to the rank-and-file fighters.
ISIS leaders are thought to be moving their families out of the cities
"We're also commonly seeing reports of ISIS arresting and executing their fighters who try to abandon the fight or are suspected of collaborating with forces trying to liberate areas that ISIS controls.
"We're hearing typical reports that ISIS leaders understand their fate in Raqqa and they're moving their own families out of Raqqa and into towns and villages in the countryside, even as they detain civilians who attempt to do the same."
Col Dorrian gave his briefing while Iraqi forces backed by Coalition aircraft stepped up their bid to retake West Mosul following the liberation of the east side of the city.
British Special Forces are thought to be involved alongside American counterparts, helping direct air strikes and advising the Iraqis.
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The depraved terror group released a photo of what is is believed to be Ronald Fiddler, known as Abu Zakariya al-Britani , who detonated a car bomb at an Iraqi army base near the Iraqi city of Mosul.
Col Dorrian said the Coalition is taking "every opportunity that we can to remove ISIS leadership figures from the battlefield".
Since the beginning of the year air strikes have eliminated three top IS commanders, including one who coordinated suicide bombers across Iraq and another who oversaw Mosul's anti-aircraft defences.
Last week a former Al Qaeda member, Haqqi Ismail Hamid al-Mmri, who terrorised civilians in Mosul as a leader of IS security networks, was killed in a precision airstrike.
Col Dorrian said: "This further loosened the grip of ISIS on the population of the city."
East Mosul has been liberated but Iraqi forces face a tough task in the rest of the city
But Col Dorrian admitted the Iraqi forces face "an extraordinarily difficult fight" to recapture West Mosul.
He said they will have to clear 100,000 buildings in a "compressed" area.
He said: "These buildings have to be cleared from rooftop level through every room, every closet, all the way down to ground level, including the tunnels that get dug between buildings. It's very, very dangerous and tedious."
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