How does the UN Convention on the Law of the Sea (UNCLOS) regulate use of force at sea?
Executive summary
UNCLOS does not itself create a general right to use force at sea; it allocates jurisdictional zones (territorial sea, exclusive economic zone, high seas) and specifies activities that affect when states may act — for example, coastal states exercise “full sovereignty” in their 12-nautical-mile territorial sea while ships on the high seas fall under flag-state jurisdiction — and UNCLOS cross‑references other law on force such as the UN Charter [1] [2]. The treaty also defines warships and immunities (Article 29/32) and contains discrete enforcement hooks — e.g., articles on piracy and the right to board or arrest in certain circumstances — but scholars and recent commentary stress gaps and uncertainties about peacetime law‑enforcement by warships and the interplay with UN Charter rules on use of force [3] [4] [1].
1. UNCLOS sets the maritime map; jurisdiction determines who may act
UNCLOS structures the sea into zones and assigns powers to states: the territorial sea (12 nm) is subject to the coastal state’s “full sovereignty,” while beyond that flag states exercise exclusive jurisdiction over their vessels in the EEZ and high seas, which matters directly for when and how a state may lawfully use force against a foreign ship [1] [2]. Legal scholars emphasize that the territorial sea rule means a state that could lawfully use force on another state’s land may also be able to do so in its territorial waters, whereas outside the territorial sea interference is limited by the flag state’s jurisdiction [1].
2. UNCLOS contains specific enforcement rules (piracy, hot pursuit, customs and pollution) but not a blanket use‑of‑force code
UNCLOS gives express rules permitting certain enforcement actions: it defines piracy and grants universal jurisdiction in those cases, provides for hot pursuit and limited boarding for violations of coastal laws, and imposes obligations for combating pollution and protecting the marine environment — but these are specific exceptions, not a carte blanche to use force generally at sea [5] [2]. Recent analysis points to Articles 29 and 32 (warship definition and immunities) and to provisions like Articles 29–32 and others cited by commentators as legal bases for maritime law enforcement, yet literature finds the law leaves gaps for peacetime law‑enforcement by warships [3] [4].
3. The UN Charter and the prohibition on the use of force remain paramount
Commentators stress that UNCLOS does not override the UN Charter’s prohibition on the use of force: where there is tension, Article 103 of the UN Charter gives the Charter priority over other treaties, and scholarship notes the Charter’s Article 2 and customary international law prohibit force unless an exception (self‑defense, Security Council authorization, or lex specialis like humanitarian law in armed conflict) applies [1]. Academic analysis therefore treats UNCLOS exceptions as limited and subordinate to the Charter’s prohibition [1].
4. Warships, “innocent passage,” and disputed practice generate controversy
UNCLOS uses conduct‑based tests for “innocent passage” and identifies activities (including use of force or military exercises) that negate innocence (Article 19), but states dispute whether and how those rules apply to warships and coast guard vessels — producing competing national positions and hot political disputes (e.g., Japan–China tensions around coast‑guard operations) [6]. The Diplomat and other commentators show persistent disagreement over whether coastal states can treat foreign warships or paramilitary law‑enforcement ships as “non‑innocent” when they assert domestic enforcement rights [6].
5. Scholars flag regulatory gaps for peacetime maritime law enforcement
Specialist literature argues that UNCLOS and older instruments give some legal bases for law enforcement (articles on high seas and enforcement) but do not fully regulate peacetime use of force by warships, creating uncertainty that states exploit or contest; authors call for implementation agreements and cross‑disciplinary rules to close these gaps [4]. The academic consensus in these sources is that UNCLOS supplies building blocks but not a comprehensive code for when force may be used by naval or coast‑guard vessels in peacetime [4].
6. What this means in practice: state practice matters and disputes land in courts or politics
Because UNCLOS leaves many practical questions open, outcomes turn on state practice, unilateral declarations at ratification, and dispute settlement or political bargaining. UNCLOS parties and non‑parties alike (the United States has not ratified UNCLOS as of sources here) navigate these rules differently and press claims in diplomatic and legal fora, which shapes who can lawfully use force at sea in concrete incidents [7] [8].
Limitations of this review: primary UNCLOS text is cited in general here [2] and academic commentary [1] [4] [3] and recent reporting [6] highlights contested interpretations; available sources do not provide a single exhaustive statutory list of every permissible use of force under UNCLOS and do not replace direct legal advice for specific incidents.