STEVE INSKEEP, HOST:
We have advance word this morning of just what the U.S. military thinks went wrong during an airstrike in Mosul, Iraq. In March, a U.S. aircraft dropped a bomb over that city. A building was below it. And when the flames died down, between 100 and 200 civilians were dead, all of this during an operation to kick ISIS out of the city. Now the Defense Department will announce results of an investigation today. And NPR's Pentagon correspondent Tom Bowman has been reporting this story.
TOM BOWMAN, BYLINE: Hey, Steve.
INSKEEP: So let's just work through this. What did the original reports of this incident say?
BOWMAN: Well, back in March, U.S. said an airstrike hit an area where civilian casualties had been reported. Now...
INSKEEP: An area where they'd been reported. So...
INSKEEP: ...Somewhere in the neighborhood, all right.
BOWMAN: Right. And that day, rescue workers were pulling dozens of bodies from this building in western part of Mosul where Iraqi fighters were trying to take the city back from ISIS fighters. Now - so you have local forces, and the U.S. is essentially serving as its air force for the local forces. And that's where we were back in March.
INSKEEP: OK. And so the Pentagon said, we've heard these reports of many civilian deaths. We'll investigate. Now that they have, what is the Pentagon version of events? From the beginning, what happened?
BOWMAN: Well, what I'm hearing - the investigation will say that Iraqi troops came under fire from ISIS snipers. The U.S. responded with an airstrike, hitting this building with a small bomb - it's about 250 pounds. And it was later learned that there were civilians in the building, you know, a couple of hundred as many. And they're not sure if they were being held hostage by ISIS or just went there for safety. Now, what the Pentagon will say is that this small bomb could not have just completely demolished the building and left a crater.
INSKEEP: I guess we should be clear. Two hundred fifty pounds is a lot of explosives, but there are much larger bombs...
BOWMAN: They consider that a small bomb.
BOWMAN: Right. So it basically left a crater. And that's what led to - you know, this building was destroyed. And the U.S. will likely say, listen, that they had no time to check who was in the building. Because these snipers were under fire, they had to act quickly.
INSKEEP: So the Pentagon is going to say, we did this because we were trying to save our Iraqi allies on the ground. That's their version of events.
BOWMAN: Absolutely, right.
INSKEEP: And the civilians were killed by the bomb that actually dropped or perhaps some other explosion, some additional explosion?
BOWMAN: That's right. They think there was a secondary explosion. This bomb hit the building, and it was either booby trapped, the building, or they were storing bombs there. And that secondary explosion completely destroyed the place and left a crater.
INSKEEP: So Tom, I have to say this version of events from the Pentagon somewhat exonerates the U.S. military in a sense. Is there an alternative version of events, alternative evidence?
BOWMAN: You know, there isn't. Iraqi forces at the time said this is likely what happened. And there were no human rights groups here at the time investigating because it's in the middle of a fight. ISIS still holds this city, and it's just hard to get in and get an independent view of exactly what happened.
INSKEEP: Is there an underlying reality here that when you're fighting in an urban area, civilians are going to be killed?
BOWMAN: Yes. That's a sad truth here - is that you have hundreds of thousands of civilians in Mosul, and they've been taking back that area block by block. And they're still doing it now. They're in the old part of the city - very narrow streets and still a lot of people there. So it's difficult. And it's going to get more difficult next door in Syria because they're getting ready to assault the city of Raqqa, the de facto capital of ISIS. You also have hundreds of thousands of civilians there as well.
INSKEEP: Well, let me ask if the rules have changed because President Trump, while campaigning, said he wanted to, quote, "bomb the hell out of ISIS." There is a perception of more civilians being killed. Is the military doing anything differently, Tom?
BOWMAN: You know, they haven't changed the rules of engagement. And Defense Secretary Jim Mattis said just last week, we're take extraordinary care to make sure that no civilians are killed. Let's listen to what he said.
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JAMES MATTIS: I want to emphasize here there has been no change to our rules of engagement and there has been no change to our continued extraordinary effort to avoid innocent civilian casualties.
INSKEEP: No change in the rules of engagement, but is there a change in aggressiveness as they push into these urban areas?
BOWMAN: They are definitely being more aggressive. There are more airstrikes. They have U.S. troops closer to the frontlines. But again, they're saying they're taking extraordinary care to watch out for any civilian casualties. But again, Steve, if you're talking hundreds of thousands of people, a well dug-in enemy - these things could possibly happen again.
INSKEEP: Tom, thanks very much as always.
BOWMAN: You're welcome.
INSKEEP: That's NPR Pentagon correspondent Tom Bowman with advance word on an investigation of an airstrike that killed civilians in Iraq. Transcript provided by NPR, Copyright NPR.