Transcript for US-led airstrike on Mosul may have killed Iraqi civilians

against ISIS, robin and american-led air strikes in moosle and accusations that the air strikes may have killed hundreds of Iraqi civilians in mosul. If confirmed this could be one of the deadliest instance of unintended death since the war began. Let's get right to Martha Raddatz. She's live with us from Washington. Martha, what do we know about what happened and has there been any shift in tack tiffs under the new president. Reporter: This was not just one building that was hit but witnesses say a city block was destroyed. I think the thing to remember is this is an urban environment. There's no more challenging battlefield than that. Some Iraqi officers said the U.S. Has been quicker to strike targets of late but the military says the rules of engagement have not changed since Donald Trump became president and what they're looking at is whether there was a secondary explosion caused by explosives left there purposefully by ISIS or whether this was just a terrible mistake, David. Martha, as you know we were all waiting for secretary of defense James Mattis to weigh in. He was asked about those civilian deaths. Reporter: He was, David. He said there is no military force in the world more sensitive to civilian casualties that they do everything humanly possible to protect innocent people, unlike ISIS. But Mattis knows firsthand having fought in Fallujah which was a packed urban environment that the enemy can hide behind women and children and that's why they're investigating to fine the truth in this case. Martha Raddatz with us this morning from Washington. Thanks, Martha.

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