GEOFF BENNETT: Defense Secretary Pete Hegseth today said no nation in the world takes greater care to avoid civilian casualties than the U.S.

But the U.S.

is currently investigating an explosion at a school next to an Iranian navy base that Iran says killed more than 150 people, mostly schoolgirls.

AMNA NAWAZ: An official briefed on the initial review tells "PBS News Hour" the strike was likely American.

Nick Schifrin examines videos and satellite images and speaks to experts for a closer look at what appears to be the deadliest strike of the war.

NICK SCHIFRIN: In the moments after the attack, the only sounds were screams.

The school where many of these parents had dropped off their children not long before is now collapsed and gutted, the scale of death clear from the air, rows and rows of tiny graves, classmates in life and now death, a victim still wearing her backpack, like in class, all lined up, a roll call of the dead.

An official brief on the initial review tells "PBS News Hour" the strike was likely American.

Video broadcast by the semi-official Mehr News Agency reportedly shows the strike and, slowed down, weapons experts say that is an American Tomahawk.

And, today, Iranian state media released these photos it said were taken at the site that appeared to show fragments of an American Tomahawk.

MASTER SGT.

WES BRYANT (RET.

), U.S.

Air Force: I could already tell, when initial reports came out on this strike, just looking at the damage, that this was a deliberately targeted strike package.

NICK SCHIFRIN: Retired Master Sergeant Wes Bryant spent 20 years in the U.S.

Air Force, where he called in airstrikes and led targeting cells and then worked in the Defense Department's Civilian Protection Center until the Trump administration reduced its size.

Bryant says this satellite image from after the attack shows six precise strikes inside an Islamic Revolutionary Guard Corps navy base.

The seventh hit the school adjacent to the base's northwest corner.

MASTER SGT.

WES BRYANT (RET.

): You have within this IRGC naval compound, which as it turns out is a missile headquarters, you have at least seven buildings within this broader compound that were struck.

These impact points were generally center of the building and they hit each of these buildings almost near perfectly.

Only the U.S.

and Israel are capable of that precision, but an Israeli official tells PBS News Hour, the Israeli Air Force was not operating in that area at that time.

And the American map of where U.S.

forces were operating indicates a target on Minab.

DONALD TRUMP, President of the United States: I will say that the Tomahawk, which is one of the most powerful weapons around, is used by -- is sold used by other countries.

NICK SCHIFRIN: Yesterday, President Trump said that Iran too has Tomahawks.

It does not, although Iran does have cruise missiles, the same technology as in a Tomahawk.

DONALD TRUMP: Whether it's Iran, who also has some Tomahawks -- they wish they had more.

NICK SCHIFRIN: On Air Force One this weekend, President Trump blamed Iran.

DONALD TRUMP: We think it was done by Iran.

They're very inaccurate, as you know, with their munitions.

NICK SCHIFRIN: From what you're seeing, could it have been an Iranian air defense missile going awry?

MASTER SGT.

WES BRYANT (RET.

): Taken in aggregate, with all of the other information we have, this targeting of the entire compound, the videos of the Tomahawk, the remnants of the Tomahawk, the hallmark of a U.S.

strike, I say that's fairly improbable at this point.

NICK SCHIFRIN: Bryant believes it is possible that the satellite image the U.S.

military used was out of date.

As seen in Google Earth, today, there is a clear wall that separates the school from the base.

But back in 2013, there was no wall.

The wall was built by 2016.

MASTER SGT.

WES BRYANT (RET.

): Potentially using targeting data that is a decade-plus-old and not updating it and not going in and verifying what's happening on the ground right now, is this still actually a military target, are there possibly civilians in it, even if it is, and how are we going to address that, none of that happened.

PETE HEGSETH, U.S.

Defense Secretary: No nation in the history of warfare has ever attempted in every way possible to avoid civilian casualties.

NICK SCHIFRIN: Today, Secretary Pete Hegseth accused Iran of placing missiles next to schools without connecting it to the girls school strike.

PETE HEGSETH: Iran, who targets civilians indiscriminately, who we've seen in the intel moving rocket launchers into civilian neighborhoods, near schools, near hospitals to try to prevent our ability to strike, that's how they operate.

NICK SCHIFRIN: But a U.S.

official says that Hegseth and DOGE cuts reduced the Pentagon's office dedicated to preventing civilian casualties by 90 percent and by two-thirds at the military's Middle East Regional Command.

What's the impact of those cuts?

MASTER SGT.

WES BRYANT (RET.

): You have a drop in -- a direct reduction in capability to characterize a civilian environment in order to properly characterize a target and conduct an assessment on risk to civilians at that target or in the general area.

And then you have a de-emphasis on the prioritization of protection of civilians.

And that's going to have a filter-down effect.

That's going to filter down to exactly how you end up executing operations.

NICK SCHIFRIN: Bryant and others are careful not to suggest the cuts led directly to civilian casualty incidents.

But, rhetorically, Hegseth has emphasized what he calls lethality over the laws of war.

PETE HEGSETH: America, regardless of what so-called international institutions say, is unleashing the most lethal and precise airpower campaign in history, all on our terms with maximum authorities, no stupid rules of engagement, no nation-building quagmire, no democracy-building exercise.

NICK SCHIFRIN: Why is it important for you to speak out today in public in case the U.S.

military did make this mistake?

MASTER SGT.

WES BRYANT (RET.

): The principles of restraint, of adherence to international law, of lessening human suffering when we do have to go to war, of the protection of civilians, these are the ideals and principles that I came up with as primary, as foundational for what we were, what we embodied as American war fighters.

They hold up the values of the American people.

And that's what separates us from those we hold as our enemies.

NICK SCHIFRIN: President Trump says he will respect the investigation's outcome of one of the deadliest strikes on civilians in the Middle East in years.

For the "PBS News Hour," I'm Nick Schifrin.