US bombs bridge in Mosul used by ISIL.

Reuters:

U.S. forces backing an Iraqi army campaign against Islamic State in Mosul carried out an air strike on a bridge spanning the Tigris river, restricting militant movements between western and eastern parts of the city, a U.S. official said on Tuesday.

U.S.-trained Iraqi Counter-Terrorism Service forces are pushing deeper into east Mosul, the last major city controlled by the Sunni hard-line group in Iraq, while army and police units, Shi'ite militias and Kurdish fighters surround it to the west, south and north.

Militants have steadily retreated into Mosul from outlying areas. The army's early advances have slowed as militants dig in, using the more than 1 million civilians inside the city as a shield, moving through tunnels, and hitting troops with suicide bombers, snipers and mortar fire.

Five bridges span the Tigris that runs through Mosul. They have all been mined and boobytrapped by militants who took over the city two years ago as they swept through northern Iraq and declared a caliphate in parts of Iraq and neighboring Syria.

Despite planting the mines, Islamic State fighters have so far been able to continue using those bridges which have not yet been destroyed by air strikes.

Air Force Colonel John Dorrian, a Baghdad-based spokesman for the U.S.-led coalition, said on Tuesday an air strike hit the number four bridge, the southernmost, in the past 48 hours.

"This effort impedes Daesh's freedom of movement in Mosul. It inhibits their ability to resupply or reinforce their fighters throughout the city," he said using an Arabic acronym for the militant group.

A month ago, a U.S. air strike destroyed the No. 2 bridge in the center of the city and two weeks later another strike took out the No. 5 bridge to the north.
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The mining and booby trapping of the bridges make them of little value to the Iraqi forces, so the bombing of the bridges to deny their use by ISIL makes some sense.   What does not make much sense is the UN's claim that bombing the bridges hampers civilian evacuation.  I suspect that one of the reasons for the boobytrapping was to make it less likely that civilians would use the bridges as well as to slow the Iraqi advance.