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Iran Update, September 17, 2026

William Doran, Ben Rezaei, Carolyn Moorman and Annika Ganzeveld

Data Cutoff: 2:00 PM ET

The Institute for the Study of War (ISW) and The Critical Threats Project (CTP) at the American Enterprise Institute are publishing updates Monday through Friday to provide analysis on the war with Iran. Most updates cover events from the past 24-hour period, whereas Monday updates also include events from the preceding weekend, collected after ISW-CTP's 2:00 PM ET Friday data cutoff. ISW-CTP may publish special updates on Saturdays and Sundays if events warrant, however.

Key Takeaways:

Allowing the Houthis to consolidate control over the Red Sea coastal plain would enable the Houthis to assert illegal authority over international maritime traffic in the Bab al Mandeb Strait, which would be extremely detrimental to US interests. The Houthis' recent military activity in the Red Sea coastal plain indicates that the group is trying to reinforce its de facto control over the Red Sea coast in tandem with its efforts to assert illegal authority over maritime traffic.
The Houthis are using their ability to threaten international shipping to deter the United States from providing more significant support to Saudi Arabia against the Houthis. The Houthis have effectively told the United States that the group will not attack international, non-Saudi vessels if the United States refrains from supporting Saudi Arabia and confronting the Houthis. This diplomatic "understanding" is intended to deter the United States from becoming more involved in the conflict by warning that the Houthis could attack international vessels if the United States supports Saudi Arabia militarily.
The current Houthi military campaign against Saudi Arabia is malignant and imposes economic costs on the entire international community, not solely Saudi Arabia. Saudi Arabia is one of the world's largest oil producers, and attacks on its major oil refineries and other facilities contribute to high oil prices worldwide.
Saudi and international attempts to restrain the Houthis through mediation or contact with Iran are unlikely to succeed because the Houthis are an independent partner of Iran that pursues discrete objectives. The Houthis' campaigns in Yemen, Saudi Arabia, and the Red Sea simultaneously advance both Houthi and Iranian objectives, which makes it further unlikely that Iran would try to “rein in” the Houthis.

Toplines

Allowing the Houthis to consolidate control over the Red Sea coastal plain would enable the Houthis to assert illegal authority over international maritime traffic in the Bab al Mandeb Strait, which would be extremely detrimental to US interests. International media has reported in recent days that the Houthis and the United States informally agreed to avoid conflict with one another following a September 13 meeting between Houthi and US representatives in Muscat, Oman.[i] A regional source familiar with the meeting told Axios on September 16 that the Houthis "committed to allow" non-Saudi vessels to transit the Bab al Mandeb Strait during the meeting, provided that the United States upholds its ceasefire with the Houthis that began in May 2025.[ii] The Houthis' pledge to "allow" non-Saudi navigation through the strait indicates that the Houthis seek to assert authority over international shipping by determining which vessels are "allowed" to transit and which vessels the Houthis would prohibit from transiting through the strait.[iii] The Houthis would likely use force against "violating” vessels, given that the Houthis have attacked several Saudi vessels in the Red Sea since July as part of the Houthi blockade on Saudi Arabia.[iv] The Houthis have made similar statements in recent weeks emphasizing that the Red Sea and the Bab al Mandeb are open to non-Saudi vessels and that the Houthis will provide "free and optional" safe passage services to these vessels.[v] Current Houthi promises to refrain from restricting international, non-Saudi maritime traffic through the Bab al Mandeb provide no guarantee that the group will perpetually refrain from attacking vessels belonging to the United States, its allies, and other Houthi adversaries.

The Houthis' recent military activity in the Red Sea coastal plain indicates that the group is trying to reinforce its de facto control over the Red Sea coast in tandem with its efforts to assert illegal authority over maritime traffic. The Houthis currently possess near-exclusive control over the Red Sea coastal plain in Yemen and major islands in the southern Red Sea following a major military offensive against the Yemeni government between September 9 and 11.[vi] The Houthis will likely exploit their control over this advantageous terrain to try to claim illegal authority over the Bab al Mandeb.[vii] Evidence of Houthi efforts to construct berms east of the Bab al Mandeb in recent days indicates that Saudi and Yemeni government efforts to deny the Houthis control of terrain along the strait have thus far been unsuccessful, and that the Houthis are preparing to defend and ensure their long-term control of this terrain.[viii]

The Houthis are using their ability to threaten international shipping to deter the United States from providing more significant support to Saudi Arabia against the Houthis. The Houthis have effectively told the United States that the group will not attack international, non-Saudi vessels if the United States refrains from supporting Saudi Arabia and confronting the Houthis.[ix] This diplomatic "understanding" is intended to deter the United States from becoming more involved in the conflict by warning that the Houthis could attack international vessels if the United States supports Saudi Arabia militarily. The United States has reportedly declined Saudi requests for direct military support against the Houthis during the current conflict.[x] US and international unwillingness to challenge current Houthi political and military activities, including the group's capture of the Red Sea coastal plain and Houthi statements that subtly assert illegal control over an international waterway, reinforces the Houthis' deterrence against the United States and its partners.[xi]

The current Houthi military campaign against Saudi Arabia is malignant and imposes economic costs on the entire international community, not solely Saudi Arabia. Saudi Arabia is one of the world's largest oil producers, and attacks on its major oil refineries and other facilities contribute to high oil prices worldwide.[xii] This economic effect impacts various global industries because petroleum is a necessary resource for producing combustible fuels, plastics, textiles, and other ubiquitous products.[xiii] These global economic costs also advance Houthi and Iranian objectives by imposing both direct pressure on Houthi and Iranian adversaries as well as indirect pressure through the international community.[xiv] Iranian decision-makers have sought to control traffic through the Strait of Hormuz throughout the current conflict in order to raise economic costs against the United States to degrade the United States’ willingness to continue the war.[xv] The Houthis have similarly attacked Saudi tankers and oil infrastructure to maximize political and economic costs in Saudi Arabia, through which the group seeks to compel Saudi Arabia to submit to Houthi demands.[xvi] Houthi demands include ending Saudi military activity and support for anti-Houthi forces in Yemen, lifting the Saudi blockade on Houthi-controlled territory, securing Saudi support for Houthi civil servant salaries, and extracting Saudi war reparations for attacks on Houthi-controlled territory.[xvii]

The Houthis are attempting to fortify their positions along the Bab al Mandeb Strait amid reports that the Yemeni government re-established control over high ground that sits above Houthi positions near the Bab al Mandeb. Houthi efforts to reinforce their positions along the Bab al Mandeb indicate that the Houthis intend to hold and defend these positions. The Houthis constructed roughly 11 kilometers of earthen berms along their frontline positions north of al Aradi, Lahij Governorate, between September 11 and 16, according to satellite imagery on September 16.[xviii] Military forces can construct berms to hastily defend a position against direct fire and enemy advances.[xix] CTP-ISW has not observed any Houthi attempts to construct structures that are typically used for a more protracted defense, such as trenches, near the Bab al Mandeb at the time of this writing.

Houthi efforts to reinforce positions by the Bab al Mandeb coincide with UK-based, Qatari-owned media reporting that the Homeland Shield Forces and Southern Giants Brigades, which are military factions that are nominally part of the Yemeni government, re-established control over Jabal Kahbub on the Lahij-Taiz Governorate border on September 17.[xx] Jabal Kahbub is a mountainous area that sits approximately 30 kilometers north of Houthi positions by the Bab al Mandeb, including the Houthis’ berms. Yemeni government-aligned forces could utilize the advantageous high ground of Jabal Kahbub to engage Houthi forces along the relatively open Red Sea coastal plain. The Houthis and Yemeni government-aligned forces previously fought over the Jabal Kahbub area on September 13 and 14.[xxi]

Saudi and international attempts to restrain the Houthis through mediation or contact with Iran are unlikely to succeed because the Houthis are an independent partner of Iran that pursues discrete objectives. Iranian sources told Reuters on September 17 that the People's Republic of China (PRC), under Saudi urging, privately asked Iranian leaders to "rein in" the Houthis following the group's offensive on the Red Sea coastal plain.[xxii] PRC Foreign Affairs Minister Wang Yi met with Iranian Foreign Affairs Minister Abbas Araghchi in Beijing on September 16, although it is unclear whether the officials discussed the Saudi request.[xxiii] These efforts incorrectly assume that the Houthis are beholden to Iranian decision-making and that the Houthis are a subordinate proxy, rather than a partner, to Iran. Characterizations of the Houthis as a proxy or solely an extension of Iran's Islamic Revolutionary Guards Corps (IRGC) distract the international community from applying meaningful pressure on the Houthis.[xxiv] The Houthis receive extensive financial and military support from Iran but are not subject to Iranian command and pursue objectives that are independent of Iranian interests.[xxv] The Houthis did not support Iran following the start of the current conflict in February 2026 by striking US and Israeli targets or threatening shipping in the Red Sea, even though Iran reportedly encouraged the group to do so, for example.[xxvi]

The Houthis' campaigns in Yemen, Saudi Arabia, and the Red Sea simultaneously advance both Houthi and Iranian objectives, which makes it further unlikely that Iran would try to “rein in” the Houthis. The Houthi campaign supports Iranian efforts to degrade the United States’ will to fight through maximizing regional partners’ economic and political costs, which Iranian leaders view as a means to influence US policymaking.[xxvii] Iranian leaders specifically calculate that imposing economic pressure on US allies will compel those allies to pressure the United States to end the conflict.[xxviii] The Houthis’ attacks on Saudi oil infrastructure and ability to directly position military assets on the Bab al Mandeb also exacerbate global economic pressures stemming from the regional conflict.[xxix] IRGC-affiliated media published an op-ed on September 17 that argued that the Houthis' territorial gains on the Red Sea coastal plain, together with Iran's "powerful presence and management" over the Strait of Hormuz, increase economic pressure on the United States and its allies.[xxx] The op-ed argued that this economic pressure provides Iran with greater bargaining power in negotiations with the United States and expands Iran’s long-term deterrence and leverage over international shipping and commerce.[xxxi] Countries like the PRC have previously failed to "rein in" the Iranian regime's attempts to control the Strait of Hormuz and forcibly regulate international shipping because Iran has little incentive to forfeit this leverage.[xxxii]

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