Story highlights Four of five bridges disabled

Iraqi-led forces surrounding city

Irbil, Iraq (CNN) The International Organization for Migration expressed concern Thursday that civilians may be trapped inside the Iraqi city of Mosul after a fourth key bridge was put out of use in a US airstrike, leaving just one to link the east to the west.

The strike was part of an ongoing Iraqi-led operation to free the city from more than two years of brutal rule by ISIS militants. Only the city's oldest bridge remains.

A Google Earth satellite images of bridges across Mosul's Tigris River before the operation.

The bridges were "disabled in order to reduce Da'esh freedom of movement and limit their ability to resupply and reinforce fighters," said Col. John L. Dorrian, spokesman for the US mission in the Mosul operation, using another name for ISIS.

The coalition coordinates all strikes with the Iraqi government ahead of time, Dorrian explained.

"The implications of disabling or damaging civilian infrastructure are carefully considered before action is taken," he said, adding that the bridges will be easily repaired after ISIS has been driven out.

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