Toplines

The Islamic Revolutionary Guards Corps (IRGC) attempted to attack US naval forces on September 5, likely to try to degrade the United States’ resolve to continue enforcing its naval blockade on Iranian ports. The IRGC Aerospace Force announced on September 5 that it targeted a US aircraft carrier and destroyer because the vessels were enforcing the US naval blockade.[1] US Central Command (CENTCOM) confirmed that Iran launched ballistic missiles at two US Navy warships but noted that the missiles did not hit the warships or cause any casualties.[2] Iranian Supreme National Security Council (SNSC) Secretary Mohsen Rezaei claimed that Iran tested a new “destroyer missile” in the attack, but ISW-CTP cannot verify what type of system Iran used in the attack.[3] CENTCOM responded to the Iranian attacks by disabling two Iranian oil tankers and destroying a third, after which Iran claimed it attacked six commercial vessels.[4] There is no evidence that Iran conducted these attacks on civilian vessels, however. The Iranian Khatam ol Anbia Central Headquarters warned on September 5 that Iran would conduct more severe attacks on US military vessels if the United States maintains its blockade.[5] Rezaei separately claimed on September 6 that a successful Iranian strike on a US warship could inflict significant US casualties, likely to try to weaken the United States’ willingness to continue to enforce the blockade by highlighting the regime’s willingness to target and inflict harm on US naval forces.[6] Iran likely calculates that raising the military and political costs of enforcing the blockade will weaken US willingness to sustain it and ultimately pressure the United States to end the blockade, thereby improving Iran’s ability to assert its claimed control over the strait and reduce economic pressure on the regime.

The IRGC may have also conducted the attack to deter US forces from facilitating the transit of commercial vessels through the strait amid indications that Iran may be facing constraints in its maritime surveillance, targeting, and mine-laying capabilities.[7] US forces have helped commercial vessels transit the southern route of the strait, which has increased traffic through the strait and undermined Iran’s effort to compel vessels to use its illegal traffic separation scheme.[8] Recent US strikes have degraded Iranian coastal radars and surveillance equipment, mine-laying capabilities, and other systems that the IRGC has relied on to monitor and threaten commercial shipping.[9] Iran has consequently adopted less effective methods, including using fast attack craft to visually identify vessels and shore-based rocket launchers to deploy mines, in its efforts to control shipping in the strait.[10] Iran may have directly threatened US naval forces to deter these forces from supporting efforts to restore freedom of navigation in the Strait of Hormuz that undermine Iran’s claimed control of the strait.

Iran’s planned restricted maritime zone appears to be a separate effort to deter commercial vessels from bypassing Iranian control of the strait and coerce the shipping industry to pressure the United States to lift its blockade. Rezaei announced on September 6 that Iran will establish a “restricted zone” extending from the US blockade line south of the Strait of Hormuz to the Persian Gulf.[11] Rezaei said that vessels entering the zone must follow Iranian transit requirements and that Iran will place violators on a “sanctions list” and restrict their future passage through the strait.[12] Rezaei stated that the zone will remain in place for as long as the US naval blockade continues, directly linking the measure to Iran’s efforts to pressure the United States to lift its blockade.[13]  

Iran appears to be trying to extend the geographic scope of rules and penalties it has already sought to impose on the shipping industry, rather than creating an entirely new system of transit regulations. Rezaei’s reference to a “sanctions list” likely refers to the Persian Gulf Strait Authority’s (PGSA) “non-compliant vessels list” rather than sanctions similar to US financial sanctions.[14] Vessels on this list can face fines, detention, or confiscation during future passages.[15] The “restricted zone” therefore appears to be an attempt to extend Iran’s existing coercive framework beyond the strait toward the US blockade line, but the transit regulations and penalties Iran intends to impose on vessels do not appear to have changed.

Iran could try to use the “restricted zone” framework to justify future vessel boardings, detentions, or seizures by framing them as consistent with Iranian maritime regulations. Iran could claim that a vessel violated its declared transit requirements and portray an IRGC boarding or seizure of a vessel as a legitimate enforcement mechanism under Iran’s interpretation of maritime law. Detaining or confiscating vessels would require Iran to use force. Rezaei clarified that Iran will not attack vessels in the “restricted zone” outside the strait but he did not rule out attacks or other coercive actions against vessels once they enter the strait.[16] 

Iran’s recent efforts to coerce the United States to lift its blockade may reflect growing regime concerns about the blockade’s impact on the Iranian economy. Rezaei acknowledged on September 6 that commercial vessels continue to transit the strait with US assistance and indicated that Iran is trying to change this situation.[17] This comment is consistent with ISW-CTP’s September 4 assessment that Iranian decision-makers appear dissatisfied with the current status of the war because the United States is having some success in facilitating the flow of oil out of the strait and oil prices have plateaued below $100 per barrel in recent months.[18] These conditions undermine Iran’s efforts to use control of the strait and high global energy prices to increase pressure on the United States. The US naval blockade and recent strikes on Iranian tankers are also significantly limiting Iran’s ability to export oil, the regime’s main source of revenue. Energy firm Kpler reported on September 7 that Iranian crude oil stored on vessels outside the blockade has fallen from roughly 90 million barrels in mid-July to about 29 million barrels, for example.[19] US economic pressure has forced the regime to take steps that risk increasing public frustration toward the regime. The Iranian government announced that it will raise third-tier gasoline prices to 100,000 rials per liter beginning on September 8.[20] A previous fuel price increase in 2019 triggered large-scale protests across Iran.[21] The regime’s decision to increase third-tier gasoline prices reflects the difficult situation the regime is in as it tries to mitigate the impacts of US economic pressure while not taking drastic economic measures that could spur domestic unrest. These conditions highlight how Iran has a growing incentive to find alternative ways to force the United States to end its blockade, including by raising the military costs of enforcement for the United States and increasing commercial costs for vessels that bypass Iranian control.