Iranian threat to close Strait of Hormuz

The recent threat by Iran to “bar foreign warships from the Gulf” raises a classic issue in the law of the sea – the legality of coastal states demanding authorization for warships to pass through their waters.  The water in question is the Strait of Hormuz, linking the Persian Gulf with the Gulf of Oman and the Arabian Sea. It is an incredibly important route for international shipping and “one of the world’s most strategically important choke points.” Apparently, the Iranian regime has warned the US navy that its vessels are not welcome in the Persian Gulf and the proposed legislation before the Iranian legislature is intended to provide a basis for preventing the passage of foreign warships.
The question of whether a coastal state can require prior authorization for warships to enter its territorial sea is one that has been around for a long time.  The fact that the 1982 Convention on the Law of the Sea is fairly unambiguous when it says that “ships of all States … shall have a right of innocent passage” (article 17(1)) has not stopped several states from reserving the right to demand prior notification or authorization for the passage of warships. Indeed, Iran was amongst those states appending a declaration to its signature to the 1982 Convention according to which “ the provisions of article 21, read in association with article 19 (on the Meaning of Innocent Passage) and article 25 (on the Rights of Protection of the Coastal States), recognize (though implicitly) the rights of the Coastal States to take measures to safeguard their security interests including the adoption of laws and regulations regarding, inter alia , the requirements of prior authorization for warships willing to exercise the right of innocent passage through the territorial sea.”  Needless to say that such claims are strongly opposed by most major maritime powers, including the United States.
The ability of a coastal state to require authorization for the passage of foreign warships would appear to even more tenuous in the case of the Strait of Hormuz which qualifies as an international strait and is therefore subject to the regime of transit passage in Articles 37-44 of the 1982 Convention.  Accordingly, “all ships and aircraft enjoy the right of transit passage, which shall not be impeded.”  The right of transit passage is significantly stronger than the right of innocent passage and there is no doubt that this provision applies to warships.  The problem for the United States is that it not a party to the 1982 Convention and there is some doubt whether the provisions on transit passage have crystallised into customary international law.  Indeed, Iran in its declaration made upon signature of the Convention makes clear its view that the right of transit passage is amongst those provisions of the Convention which “ are merely product of quid pro quo which do not necessarily purport to codify the existing customs or established usage (practice) regarded as having an obligatory character.”  The statement continues, “[t]herefore, it seems natural and in harmony with article 34 of the 1969 Vienna Convention on the Law of Treaties, that only states parties to the Law of the Sea Convention shall be entitled to benefit from the contractual rights created therein.”  Again, the United States and most major maritime powers take the opposite view but this is a clear example where the failure of the United States to become a party to the 1982 Convention puts it on the back foot, having to justify its behaviour against the more contested rules of customary international law, rather than against clear treaty provisions.