GEOFF BENNETT: Yemen appears to be sliding back toward all-out war after Houthi rebels backed by Iran seized the key port city of Mokha from allies of the internationally recognized government.

Mokha sits on the Bab al-Mandab, a critical shipping choke point and gateway to the Red Sea.

Nick Schifrin has more on the escalating conflict, which is pushing oil prices higher and raising fears of a wider regional war.

NICK SCHIFRIN: In Yemen today, a Houthi advance that once again threatens a global fault line.

Iran-backed Houthi fighters chanted death to the U.S.

and Israel as they walked into a government building today and released these videos of Central Mokha, seizing Western armored vehicles, releasing prisoners held by Yemeni government allies, and on a joyride on the Mokha Airport.

This is territory that's been contested for more than a decade.

For weeks, the fighting's been simmering.

Saudi-backed Yemeni fighters have tried to hold the line.

But they have been pushed back quickly, as the Houthis have captured a string of positions in Yemen leading to Mokha, which sits on Yemen's coast just a short distance from the Bab al-Mandab, the 20-mile-wide gateway to the Red Sea.

It was already one of the world's most important maritime choke points, more so since Iran has maintained its choke hold on the Strait of Hormuz.

Already, the Houthis had been threatening Saudi ships, and they attacked key Saudi energy and military facilities across the border.

Saudi officials say the Houthi attacks have destroyed civilian homes and wounded more than 70 people.

MOHAMED A-BUKHAI, Houthi Spokesperson (through translator): The fight for the west coast of Yemen had to be decisive.

We are very keen to face the enemy directly.

The next step would be to get into a dialogue that involved the political and leadership parties in Yemen.

NICK SCHIFRIN: I spoke remotely today to Houthi spokesman Mohamed A-Bukhai.

You're calling for dialogue, but are you planning to expand the military operation?

Will you try and seize more territory alongside the Bab al-Mandab?

And will you also try and seize Perim Island inside the Bab al-Mandab?

MOHAMED A-BUKHAI (through translator): We don't need to actually take control over Bab al-Mandab or the island.

Our missiles can reach any ships in the sea.

NICK SCHIFRIN: The Houthis and Saudis fought a nearly decade-long war that for the last four years has been in a tentative cease-fire.

The current tensions spiked in July when Saudi Arabia bombed a Houthi-controlled airport to prevent an aircraft landing that the Saudis say was carrying Iranian weapons.

There are reports that there are IRGC members in Yemen helping direct or assist in some of these attacks.

How much of this are you doing on behest of Iran?

MOHAMED A-BUKHAI (through translator): There are no Iranian forces in Yemen.

We actually depend on ourselves to manufacture all kinds of weapons, whether they are an AK rifle or a drone or even a hypersonic ballistic missile.

NICK SCHIFRIN: Tonight, the U.N.

special envoy for Yemen, Hans Grundberg, warned, the new violence was dragging Yemen back into civil war and toward a regional conflict.

HANS GRUNDBERG, U.N.

Special Envoy for Yemen: This renewed war should alarm us all.

It effectively marks the end of the relative calm that Yemen has experienced for over four years since the U.N.-brokered truce.

It not only threatens to plunge Yemen into a prolonged and expanding war, but also risks yet again dragging the country into the wider and unresolved regional confrontation with global repercussions.

NICK SCHIFRIN: And, today, the Houthi advance pushed the price of Brent crude above $105 a barrel over concerns of disruption to global supply routes.

For perspective on the latest development in Yemen, we turn to Gregory Johnsen.

He is a longtime Yemen expert currently with the Arab Gulf States Institute in Washington, D.C.

Gregory Johnsen, thanks very much.

Welcome back to the "News Hour."

As I just mentioned, the Houthis have already been threatening Saudi ships going through the Bab al-Mandab.

You heard the Houthi spokesperson there saying that their missiles and drones can cover all of the territory in the Bab al-Mandab.

So how significant is it that they have now captured the port city of Mokha?

And I'm going to bring up the map here to understand its geography.

GREGORY JOHNSEN, Arab Gulf States Institute: Yes, thanks, Nick, and always a pleasure to join you.

It's an incredibly significant development in Yemen.

So the Houthis, as you can see there on the map, had territory on Yemen's western coast.

That was the north.But the Bab al-Mandab in the Red Sea sort of acts as a funnel, so it narrows down to about 19 miles across at its narrowest point.

That's a choke point for the Houthis.

So by moving south and taking Mokha, the Houthis are actually able to project a lot more power into the Red Sea.

So you have boats that are sort of congested there at the choke point.

This gives the Houthis more targets to aim at.

They say they're only going after Saudi oil tankers at the moment.

And it gives the ships less room to navigate.

It also allows the Houthis, at least on the defensive, to then spread their mobile missile launchers, some of the drone launchers that they have out across more territory, more geography, which makes hitting those, which was already a very difficult task, even more and more difficult, as we're seeing sort of on the other side of the Arabian Peninsula in the Strait of Hormuz.

NICK SCHIFRIN: And you just referred to more territory.

You heard the Houthis spokesperson claim that they don't want more territory.

But it does seem like that they're pushing not only into Mokha, but down along the coast and could threaten these islands that are in the Bab al-Mandab, right?

GREGORY JOHNSEN: Yes, absolutely.

I think that's what the Houthis are going to do.

I mean, for a long time, for the past several years, they have been trying to move east inland to get some of the oil and gas reserves that Yemen has, because the Houthis, while they control a lot of territory in Yemen, they don't actually have sort of the economic base to survive long term.

What's changed recently is the Houthis looking at what Iran has done in the Strait of Hormuz and saying to themselves, we can do something similar.

So, now instead of sort of pushing all their resources east toward Marib, where the Saudi air defenses and the Saudi air force was able to sort of push them back, now the Houthis are pushing their forces south along the coast to try to really take control of most of the Bab al-Mandab.

And the Yemeni national forces, the sort of anti-Houthi coalition, which was in Mokha, has withdrawn, but they have not withdrawn south.

They have withdrawn inland, which means that the Houthis can continue their advance, and there's really not that much to stop them, at least on the ground.

NICK SCHIFRIN: So let's talk about how capable or not the Yemeni government and its allies are to be able to stop the Houthis.

A senior U.S.

government official pointed out to me today that the U.S.

had assumed that the particular militia guarding Mokha was actually one of the more capable allies of the Yemeni government.

So what does it say that that militia wasn't able to defend Mokha?

GREGORY JOHNSEN: Yes, there's a long backstory here, Nick.

So, the guy who is in charge of that force in Mokha is a guy by the name of Tareq Saleh.

That name may sound familiar to some of your viewers because his uncle was the former President Ali Abdullah Saleh.

For the first few years of this war, from about 2015 to 2017, Tareq Saleh actually fought with the Houthis.

It was only when the Houthis killed his uncle, the former president of Yemen, that he defected and joined this anti-Houthi coalition.

That's one piece.

The second piece is, that late last year, Saudi Arabia really pushed the United Arab Emirates out of Yemen.

And Saudi Arabia then basically tried to take all of the various militia groups that the UAE had been supporting in Yemen, one of which was Tareq Saleh's force, and bring them under the Saudi umbrella.

So, really, what's happening on the ground is that what we call the anti-Houthi coalition or these the Yemeni national forces or whatever term we want to apply to them, we think of them as one group.

They're not one group.

They're about eight to 10 different groups, all of which are riven with infighting and bickering.

They have diametrically opposed views about what -- the end state that they actually want to see in Yemen.

And so it's not at all surprising, at least to me, and I don't think it should be to the U.S.

official, that this group was driven out of Mokha.

They -- the Houthis are experts at exploiting some of these fissures and the fractures that exist within the anti-Houthi coalition.

They have been doing it for over a decade now, and now they're putting their forces south, and they were able obviously to take the port city.

And it looks like they're going to continue to advance farther south.

NICK SCHIFRIN: We heard the U.N.

today warn that Yemen is headed towards civil war.

At what point do the Saudis reenter this war?

At what point does this become yet again a regional conflict?

GREGORY JOHNSEN: Well, I think Yemen has been in a civil war for several years, and Saudi Arabia's been involved.

Saudi Arabia was bombing targets in Yemen in July and in August as well.

The real choice that Saudi Arabia faces right now -- and we're in September of 2026 -- it's the same -- it's the same choice that Saudi Arabia faced in March of 2015, when they initially made the decision to go into Yemen.

And that is, they want to defeat the Houthis.

They want to get the Houthis out of Yemen, or at least out of Sanaa, and put what passes for the internationally recognized government back in the capital.

What Saudi needs to do that, though, is actual troops on the ground, because the Yemeni forces, as we have seen overnight with their loss of Mokha, aren't capable of defeating the Houthis on their own.

Saudi airpower isn't capable of defeating the Houthis on their own.

So we need some foreign ground troops.

But Saudi Arabia doesn't want to put foreign ground troops into Yemen for any sort of a long, bloody conflict with no guarantee of success.

And so they rely on the next best option, which is basically bombing and hoping.

And that appears to be what it is that we're headed back to, where Saudi will carry out some airstrikes, the Houthis will absorb some airstrikes, they will still make some gains on the ground, and the problem itself won't be solved.

So, essentially, we're in a situation where the Saudis know what it is that they want.

They know the objective, getting the Houthis out, but they are not willing to pay the price that it would actually cost to bring about that objective.

NICK SCHIFRIN: Gregory Johnsen, thank you very much.

GREGORY JOHNSEN: Thanks so much.