Part of an Old Debate Between the U.S. and Iran About the Strait of Hormuz: "Ships in Gulf should use Iran-defined routes"

Iran lays out its long-held contention that Iran has the right to control shipping entering the Arabian Gulf as reported by an Iranian "news" source in Ships in Gulf should use Iran-defined routes: official

In comments at a conference of maritime organizations in Tehran on Tuesday, Rear Admiral Fadavi said the Supreme National Security Council has passed a new regulation obliging all foreign ships, including American and British vessels, to take the waterway defined by Iran.

American vessels obey the Iranian rules when it comes to exercising sovereignty in the Persian Gulf, he said.

The general added that foreign vessels in the Persian Gulf do not dare to violate Iran’s instructions on the waterways.

He further explained that Iran Ports and Maritime Organization has the authority to announce the decision on new maritime routes, in accordance with the administrative and international regulations.

General Fadavi also expressed the IRGC’s readiness to detect and document environmental violations in the Persian Gulf through aerial and naval patrolling, as soon as the Ports and Maritime Organization and Iran’s Department of Environment authorize the IRGC forces.

In remarks in June 2016, Leader of the Islamic Revolution Ayatollah Seyed Ali Khamenei underlined that security of the Persian Gulf region comes within the purview of the regional countries alone, and dismissed the US claim of seeking security in the region.

“The Persian Gulf security relates to the countries of the region which have common interests, and not to the US. So, security of the Persian Gulf region should be provided by the countries of this region itself,” the Leader said.
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As Professor James Kraska noted in his 2013 article in the Virginia Journal of International Law, "Legal Vortex in the Strait of Hormuz," the issue is complicated by the fact that neither Iran nor the U. S. is a party to the United Nations Convention on the Law of the Sea (UNCLOS) which has a specific section pertaining to straits like the Strait of Malacca or, in this instance, the Hormuz Strait.

The standoff is especially complicated because the United States and Iran are not parties to the United Nations Convention on the Law of the Sea (UNCLOS).4 Both states have bypassed UNCLOS, the one multilateral treaty positioned to resolve their differences. Their status as holdouts colors every aspect of the bilateral legal relationship in the Strait of Hormuz. Their dispute is also layered and made more complex by both states subscribing to some terms of the treaty, but rejecting others. Without adherence to a common rule set, the rivals embrace incompatible views of the
source and content of the laws that govern passage through the strait.

As we now see in the South China Sea, part of the problem lies with there being two distinct types of passage through "territorial" waters, (1) innocent passage and (2) transit passage, with very different rules in play.

Under UNCLOS, a coastal state may declare an area out to 12 miles as "territorial sea." Under older law, the traditional "limit" of such claims was 3 miles. As Dr. Kraska puts it,

Ships of all nations enjoy the right of innocent passage through the territorial sea.9 On the other hand, coastal States have broad and durable security interests in the territorial sea, and may prescribe and enforce laws that condition or preclude altogether the surface transit of foreign warships.

When overlapping territorial seas connect one area of the high seas or exclusive economic zone (EEZ) to another area of the high seas or EEZ, this also constitutes a strait used for international navigation under the terms set forth in UNCLOS.10 States are entitled to exercise the right of transit passage through such straits used for international navigation. The regime of transit passage affords more rights to users of the strait than innocent passage. In most circumstances, innocent passage can be suspended by the coastal State; transit passage cannot be suspended. Transit passage also allows submerged transit and overflight of aircraft through the strait.11 Only surface transits are permitted for ships engaged in innocent passage. In the absence of acceptance of UNCLOS, however, the United States and Iran cannot use these clear rules as a guide and therefore must revert to legacy treaties, such as the 1958 Convention on the Territorial Sea and Contiguous Zone (Territorial Sea Convention), 12 as well as customary international law, to determine their respective rights and duties in the strait.

As Iran would have it, unless a country has become a party to UNCLOS, there is no "transit passage" available to it. On the other hand, Iran also asserts it has the right to a 12 mile limit on its territorial waters. Using these two concepts, Iran argues that it has the right, applying rules applicable to "innocent passage" to control the "surface transit of warships."

The counter-argument is that, in order to invoke UNCLOS benefits (the 12-mile limit), you have to accept the totality of UNCLOS without "cherry-picking" those rules that benefit you while ignoring those that don't. Thus, if Iran wants to claim that "transit passage" not applicable in its "territorial sea" it is restricted to a 3 mile limit. Again, Dr. Kraska:

Iran is not a party to UNCLOS, and therefore is under no compunction to recognize legal regimes therein unless they have become customary law and therefore binding on all nations. Since Iran is not a party to UNCLOS, it does not enjoy a twelve nautical mile territorial sea and instead may claim only the historic three nautical miles.

While restricting Iran's territorial seas can be fun, the U. S. has its own issues with UNCLOS and has to fall back on asserting that "transit passage" rights are founded in customary international law which apply even if UNCLOS does not.

Since the United States is not party to UNCLOS, it does not automatically enjoy the right of transit passage through straits used for international navigation if the coastal state also is not a party to the treaty. The United States counters that although the regime of transit passage through straits used for international navigation is reflected in UNCLOS, it springs from customary international law, rather than being a creation of the terms of the treaty. Although transit passage is codified in article 38 of UNCLOS, it merely reflects long-standing state practice and opinio juris.
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According to this view, even though the United States is not a party to UNCLOS, therefore, it nonetheless enjoys the right of transit passage through international straits as a matter of historical practice and a history of legal obligation among states. To put a final point on it, the United States rejects Iran’s claim of broad security competence over the territorial sea, since even article 16(4) of the 1958 Territorial Sea Convention precludes the coastal State from suspending innocent passage.

At the very least, it is better to say that dispute is not going to be readily resolved, though it is of vital import in a area of potential conflict. Both sides will argue their positions with vigor, but as Professor Kraska concludes in his article:

A coastal State, such as Iran, may not select a twelve nautical mile territorial sea over waters forming a strait used for international navigation, dispense with the navigational regime of transit passage, and instead insist on enforcement of innocent passage any more than the United States could recognize only a three nautical mile territorial sea and then demand to exercise the right of transit passage within it. Ultimately, it is unclear which of the two nations has the superior position to determine this legal landscape. Both the twelve nautical mile territorial sea and the right of transit passage through international straits have either entered, or are on the cusp of, customary international law. The barest tinge of irresolution to the matter means the onus is on Iran either to accept the post-1982 legal status quo or raise it as a challenge before a competent international tribunal.

Also of interest Iran's Maritime Claims.