A gunman holds an IS flag on the streets of Mosul after the group seized the city in June 2014.

In the city of Mosul, northern Iraq, Islamic State (IS) fighters clearly understand that they may be about to be attacked.

Therefore, IS is urgently reinforcing the defense system of the city, where they took control more than two years ago, according to the Niqash news site.

Build a retaining wall

Locals said that over the past two weeks, convoys of heavy vehicles and construction machinery have been operating non-stop in Mosul.

`City council trucks carry concrete shields to the peripheries. Large cranes continuously unload these shields and they are arranged similar to how the Iraqi army did before when they

Witnesses in Mosul confirmed that on the southern edge of the city, around areas such as Mamoun, Tal al-Rumman or Mansour, IS has built a concrete wall up to three meters high.

Some said similar walls also appeared on the eastern edge of Mosul, near the areas of Somar, Dumez and Falastin.

However, as the second largest city in Iraq, after Baghdad, with more than two million residents, Mosul is so large that IS has no way to build a wall around it.

According to local residents, when they first entered Mosul in mid-2014, IS boastfully announced that it would dismantle all the concrete fences that the Iraqi army placed around the city because they were no longer needed.

An IS truck inside Mosul.

Trench battle

`War is coming and the survival of our caliphate depends on Mosul’s resilience in confronting the infidels,` a Muslim cleric, about 30 years old, said during the conversation.

`Have you heard about the battle of Muslims led by Prophet Muhammad in 627? Did you know they won that battle? The people followed Muhammad and did not betray him. That

The battle that the cleric mentioned above is also called the Battle of al-Khandaq (Battle of the Trench).

On social networks, IS members also compared the upcoming battle in Mosul with the Battle of the Trench to boost people’s morale.

Previously, IS tried to dig a trench 10 km from the city border, but then the group had to stop due to continuous bombardment by coalition aircraft, causing many motor vehicles to be destroyed.

Like shield walls, trenches cannot completely surround Mosul, but they appear to be connected to a secret tunnel network that IS is building.

But even people living in Mosul today know that whoever controls the airspace will dominate the battle.

A German soldier is training soldiers of the Kurdish armed forces in the city of Erbil, near Mosul.

See more: IS leader’s secret talks to establish an Islamic empire

Hong Van