Of course international law is not worth the paper its written on.
https://en.wikipedia.org/wiki/Blockade
> Blockades restrict the trading rights of neutrals, who must submit for inspection for contraband, which the blockading power may define narrowly or broadly, sometimes including food and medicine.
They would be allowed to blockade neutral ships going to enemy ports (e.g. Israel) subject to a bunch of rules but that doesn't seem to be what they are doing.
I dont even think Iran is claiming this is a blockade. They are claiming its part of its territorial waters, and they are claiming that they dont recognize the UNCLOS which would give vessels transit rights (but at the same time they are claiming they recognize the part of UNCLOS that allows claiming 12 miles out as territorial waters). At least that is what i got from https://www.ejiltalk.org/the-legality-of-irans-closure-of-th...
Firing on neutral shipping is not the same as intercepting it and inspecting it for war materiel or other contraband. Preventing shipping from reaching or leaving Kuwaiti ports is not the same as inspecting it for war materiel or other contraband.
