Satellite images of Mosul have revealed how Islamic State fighters have dug in and built a string of barricades in readiness for the assault by Iraqi-led forces on the militant stronghold.

The pictures, released by the geopolitical intelligence company Stratfor and taken on 31 October, show the line of defensive positions constructed along the city's southern edge.

Image: Key routes into the city have been blockaded. Pic: Stratfor.com/Airbus

Buildings have also been destroyed south of their positions around Mosul International Airport to enable the jihadists to spot advancing government troops.

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Iraqi soldiers, Shia militias, Kurdish peshmerga fighters and other groups backed by US-led coalition airstrikes launched their campaign to retake Mosul last month.


Government forces entered the outskirts of the city, held by IS since 2014, on Tuesday.

Image: Concrete blocks have been used to build barricades. Pic: Stratfor.com/Airbus

The operation to retake Mosul is expected to take weeks if not months, with the prospect of house-to-house fighting through booby trapped buildings.

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The advance is complicated with around a million civilians still within the city.

IS leader Abu Bakr al Baghdadi has said in a speech there could be no retreat in a "total war" and told fighters they had to remain loyal to their commanders.

Image: The defences present a 'substantial tactical challenge', says Stratfor. Pic: Stratfor.com/Airbus

According to Stratfor, barricades built across key routes into the city have been made out of concrete blocks and other rubble, possibly from the concrete walls of destroyed buildings.

Roads still open in other locations have been lined with a stockpile of material, said Stratfor, which could "easily be tipped" as opposition forces approach.

Image: Roads have been blocked north of the airport. Pic: Stratfor.com/Airbus

The militants' defences present a "substantial tactical challenge" for advancing forces, said Stratfor.

It added government forces would need to adjust their course if they want to avoid the risk of facing dug-in IS-fighters head-on or risk crossing open terrain.

Image: The barricades will slow the advance of Iraqi-led forces. Pic: Stratfor.com/Airbus

Just north of the airport, a large number of obstacles have been placed in a series of roads.

Nearly all of the buildings in the airport complex and the former military base to its west have been destroyed, Stratfor said.