Pretty much everyone agrees that 12 nautical miles is the edge of territorial waters; whether they're bound by the UNCLOS or not.
The UNCLOS Part II Section 2 Article 3 [1] states:
> Every State has the right to establish the breadth of its territorial sea up to a limit not exceeding 12 nautical miles, measured from baselines determined in accordance with this Convention.
It does not restrict this to member states or signatory states or etc. I don't know that the UNCLOS is binding on member states while operating in the territorial waters of non-member states, but I don't think there's a compelling reason to think territorial waters of non-members are limited to 3 nautical meters, given the consensus is territorial waters are 12 nautical meters.
> Iran passed its own law in 2003 claiming 12nm. They can only assert that claim through violence.
As a member state of the UN, they can assert a claim about territorial waters against another state at the International Court of Justice. It would seem to be a question of international law. If they were a member state of the UNCLOS, there are additional dispute resolution mechanisms available. Of course, violence is always an option for dispute resolution.
The UNCLOS Part II Section 2 Article 3 [1] states:
> Every State has the right to establish the breadth of its territorial sea up to a limit not exceeding 12 nautical miles, measured from baselines determined in accordance with this Convention.
It does not restrict this to member states or signatory states or etc. I don't know that the UNCLOS is binding on member states while operating in the territorial waters of non-member states, but I don't think there's a compelling reason to think territorial waters of non-members are limited to 3 nautical meters, given the consensus is territorial waters are 12 nautical meters.
> Iran passed its own law in 2003 claiming 12nm. They can only assert that claim through violence.
As a member state of the UN, they can assert a claim about territorial waters against another state at the International Court of Justice. It would seem to be a question of international law. If they were a member state of the UNCLOS, there are additional dispute resolution mechanisms available. Of course, violence is always an option for dispute resolution.
[1] https://en.wikisource.org/wiki/United_Nations_Convention_on_...