Displaced Sunni people fleeing the violence in Ramadi, cross a bridge on the outskirts of Baghdad.

As Iraqi forces close in on the western city of Ramadi, thousands of civilians are effectively being held hostage inside by ISIS militants who want to use them as human shields.

Iraqi forces cut the hardline group’s last supply line into Ramadi in November, surrounding the city and making it almost impossible for the militants to send in reinforcements.

But for thousands of residents who remain trapped inside the mainly Sunni city, life has become even harder as the militants grow increasingly paranoid, residents said.

Reuters spoke to five residents inside the city and three who recently managed to get out. All said conditions inside had deteriorated to their worst since Islamic State overran it earlier this year.

“Daesh fighters are becoming more hostile and suspicious. They prevent us from leaving houses. Everyone who goes out against orders is caught and investigated,” said Abu Ahmed. “We feel we’re living inside a sealed casket.”

Ramadi, a provincial capital in the fertile Euphrates valley just a short drive west of Baghdad, was ISIS’s biggest conquest since last year, and reversing it would be a major victory for the Iraqi government and its spectrum of allies that include both the United States and Iran.

The description of harsh rule by ISIS fighters could also indicate disquiet among Sunni Muslim residents, some of whom switched sides to help U.S. forces defeat a precursor of ISIS in the city during the American occupation nearly a decade ago.

Sheikh Khatab al-Amir who is still in contact with members of his tribe inside Ramadi said the insurgents were restricting movement there.

“The insurgents have sectioned Ramadi into a group of smaller segments and do not permit the passage of civilians from one area to the other because they suspect anyone at the moment of being an informant for the security forces,” he said.

More people were cooperating with the security forces as the insurgents’ treatment became harsher, the sheikh said.

Residents say the militants have increased motorcycle patrols inside the city to catch those using mobile phones, which are banned in ISIS territory. High, empty buildings are also under surveillance.

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