A new memorandum of understanding between the United States and Iran could have far-reaching consequences for global maritime law and the principle of freedom of navigation, according to analysis by an expert from the Stockholm International Peace Research Institute (SIPRI). The commentary warns that language in the agreement may open the door to restrictions in the Strait of Hormuz, one of the world’s most strategically important shipping corridors.
The agreement, signed on 17 June, is intended to pave the way toward ending a conflict between the United States and Iran that began earlier this year following a wave of strikes on Iranian targets. While the pact is described as fragile, its provisions on maritime transit have drawn particular scrutiny due to their potential implications for international shipping rights.
At the center of the concern is the Strait of Hormuz, a narrow waterway connecting the Gulf to the Gulf of Oman through which a significant portion of global maritime trade passes. The SIPRI expert notes that under international customary law, ships transiting the strait are entitled to what is known as “non-suspendable innocent passage,” a legal principle that guarantees continuous and unhindered transit through international straits.
This regime, the commentary explains, is rooted in long-standing international legal practice and has been recognized by international judicial precedent, even though Iran is not a party to the United Nations Convention on the Law of the Sea. While coastal states such as Iran and Oman retain authority over safety and environmental regulation within their territorial waters, they are not permitted to obstruct the passage of commercial or military vessels engaged in peaceful transit.
The analysis focuses on a specific provision of the so-called Islamabad Memorandum, which states that Iran will ensure the safe passage of commercial vessels for a period of 60 days following the signing of the agreement. After that period, the text leaves open the possibility of new arrangements to govern maritime services and navigation through the strait.
According to the SIPRI commentary, this wording could allow Iran to introduce charges or tolls for vessels transiting the strait after the initial period. Such a development, the expert argues, would effectively make passage conditional and could conflict with the established principle of non-suspendable innocent passage under international law.
The memorandum also calls for dialogue between Iran, Oman, and other regional coastal states to define future administration of the strait in accordance with international law and sovereign rights. However, the analysis highlights that domestic legal interpretations in both Iran and Oman have previously included requirements for prior authorization for certain military vessels, raising questions about how navigation rights could be applied in practice.
The United States has historically positioned itself as a leading defender of freedom of navigation in international waters, conducting diplomatic protests and military operations in response to perceived restrictions by coastal states. The SIPRI expert notes that this longstanding policy includes decades of operational assertions in contested maritime regions, reflecting a consistent US emphasis on maintaining open sea lanes.
Against this background, the signing of the memorandum is interpreted as potentially signaling a shift in US legal and strategic positioning. The commentary suggests that if a final peace treaty were to accept restrictions on passage through the Strait of Hormuz, it could represent a departure from traditional US policy on freedom of navigation and innocent passage.
The broader implications extend beyond the Gulf region. The analysis warns that any acceptance of restrictions in Hormuz could set a precedent for other maritime disputes, including contested waters in the South China Sea and Arctic shipping routes. Such a precedent, it argues, could encourage other states to assert similar limitations on international shipping corridors, potentially undermining established maritime norms.
Given that the majority of global trade is transported by sea, the commentary emphasizes that restrictions on key straits could have significant economic consequences, including disruptions to supply chains and increases in commodity prices. The Strait of Hormuz, in particular, is described as critical to global energy flows, with past tensions in the region already demonstrating the sensitivity of oil markets to disruptions in navigation.
The analysis also considers a possible expanded role for Europe in safeguarding maritime freedom of navigation should US policy shift. It suggests that the European Union and its member states could take on a more active role in challenging what are described as excessive maritime claims, while strengthening legal and operational mechanisms to uphold international law at sea.
Proposals referenced in the commentary include the creation of a European-led legal digest of international maritime practice and the expansion of existing naval operations designed to protect shipping lanes in strategically important regions. These measures, it argues, would reinforce Europe’s position in defending the global maritime legal order.
The SIPRI expert concludes that the evolving language of the US–Iran memorandum, particularly its provisions on the Strait of Hormuz, raises significant questions about the future interpretation and enforcement of freedom of navigation. As negotiations continue toward a potential final agreement, the issue remains central to broader debates over international maritime law and global security architecture.
