How has the International Tribunal for the Law of the Sea ruled on innocent passage and interdiction?
Executive summary
The International Tribunal for the Law of the Sea (ITLOS) has repeatedly affirmed that coastal States must allow innocent passage of foreign ships but may act against passages that are not “innocent,” and that coastal States exercise full legislative and enforcement jurisdiction in their territorial sea subject to that duty [1] [2]. ITLOS’s broader jurisprudence and advisory work — including its 2024 advisory opinion linking climate-related harms to marine pollution — shows the Tribunal interprets UNCLOS expansively while recognizing limits on enforceability and detail in implementation [3] [4].
1. ITLOS’s clear baseline: innocent passage is the rule
ITLOS’s public statements and its advisory reasoning treat the right of innocent passage as a fundamental obligation of coastal States: ships of all States enjoy the right of innocent passage and coastal legislation and enforcement in the territorial sea must be exercised subject to that obligation [1] [2]. That baseline echoes UNCLOS text and ITLOS materials that position navigation rights — including innocent and transit passage — squarely within the Tribunal’s remit [5].
2. Non‑innocent passage is the exception that permits action
ITLOS sources stress that States “may take action only against passage which is not innocent,” drawing a sharp distinction between routine navigation and activities that breach the conditions of innocence set out in UNCLOS. Where passage becomes non‑innocent — for instance by threatening peace, security, or the coastal State’s laws — coastal States retain the authority to interdict or detain, subject to legal limits [1].
3. Territorial jurisdiction is full but constrained by international law
ITLOS (as summarized in legal commentaries) and its advisory materials underline that coastal States have “complete legislative and enforcement jurisdiction in their territorial seas” but that this jurisdiction operates “subject to the rule of international law,” namely the obligation to permit innocent passage [2]. In practice, ITLOS frames coastal measures as lawful only where they do not unlawfully deny or unduly hinder the right of innocent passage [2].
4. Suspension and prior‑permission practices remain contested
UNCLOS itself allows temporary suspension of innocent passage in specified areas (Article 25), a route coastal States sometimes invoke [6]. ITLOS and commentators have been drawn into disputes where coastal practices — for example, prior‑permission systems for warships asserted by some States — are criticized as inconsistent with UNCLOS’s “ships of all States” language and the Tribunal’s interpretation of freedom of navigation [7] [1]. Competing state practices and legal theories therefore leave room for litigation and advisory clarification [7] [6].
5. ITLOS’s casework illustrates enforcement remedies but also procedural limits
ITLOS’s dispute jurisdiction has produced orders for prompt release and compensation when it found coastal measures violated freedom of navigation — demonstrating the Tribunal will enforce UNCLOS protections when states litigate — but the Tribunal’s remedial reach depends on parties bringing claims and on the forum chosen under UNCLOS provisions [5]. The Tribunal’s internal procedures and rules also shape what remedies or clarifications emerge in any specific case [8].
6. Advisory opinions expand meaning but do not prescribe implementation
ITLOS’s 2024 advisory opinion, while not about innocent passage per se, shows the Tribunal’s willingness to interpret UNCLOS broadly — finding greenhouse gas emissions can qualify as marine pollution and that States have duties to mitigate and adapt — yet the opinion stopped short of detailed enforcement prescriptions, leaving substantive implementation to states and cooperation mechanisms [3] [4]. This pattern signals ITLOS will articulate legal principles on navigation and interdiction but typically will not set granular operational rules for coastal authorities.
7. Two plausible futures: litigation clarifies or state practice hardens
One path is further ITLOS adjudications and advisory work that refine what counts as non‑innocent passage, and what interdiction measures are permissible — similar to how prompt‑release cases have clarified enforcement limits [5]. The other is continued variance in coastal practice (suspensions, prior‑permission regimes) forcing states, flag States, and regional bodies to litigate or negotiate outcomes — a contest already visible in academic and policy debates [7] [6].
Limitations and sources: This analysis is based on tribunal statements, ITLOS materials, commentary and reporting provided in the supplied sources; available sources do not provide verbatim recent ITLOS judgments specifically titled as “innocent passage” cases beyond the general statements and related scholarship cited above [1] [5] [2].