Probe: U.S. set off IS bombs in Mosul

Washington — The United States acknowledged Thursday that bombing an Iraqi building in March set off a series of Islamic-State planted explosives, resulting in more than 100 civilian deaths and underscoring the difficulty of rooting out the extremist group’s fighters from its remaining urban strongholds.

The bomb dropped on a building in the city of Mosul set off explosive materials that IS militants already had been placed inside, causing the structure to collapse, the Pentagon said in describing the conclusion of a twomonth investigation. The civilians inside were seeking refuge.

The bombing led to the largest single incident of civilian deaths in the nearly 3-year-old campaign. And it illustrates the difficult urban fight U.S. and coalition forces are encountering, including what U.S. officials describe as IS militants deliberately enticing attacks on buildings where they’ve staged explosives and know civilians are inside. The civilians either enter unwittingly or are forced in and locked up.

The conclusion, said U.S. Air Force Brig. Gen. Matthew Isler, is that while the U.S.-led coalition takes responsibility for the airstrike, “a coalition munition was not responsible for the structural failure of the building and the deaths of the civilians inside.” He said IS has tried to set up similar incidents since then, prompting Iraqi and coalition forces to adjust combat tactics and watch locations more carefully in advance of strikes.

The battle for Mosul is key to eliminating IS from Iraq. But it has grown riskier for civilians as the battleground shrinks in the highly populated older section of the city. Humanitarian officials have predicted civilian casualties would spike as more than 400,000 civilians were trapped in the city’s west. A similar scenario could emerge in IS’s self-declared capital of Raqqa, Syria, which U.S.-backed militia are expected to start trying to retake soon.

In a telephone briefing with Pentagon reporters, Isler said the 500-pound precision-guided bomb dropped by a U.S. aircraft on March 17 was intended to kill two IS snipers who posed a threat to Iraqi counterterrorism forces.