Yup. His TRUTH was all ships. But what it is in practice appears to be sanctions enforcement.
I am rusty on UNCLOS but first 12 miles (nautical) is territorial. It's a sovereign part of the state. The next 12 miles, the contiguous zone is all territorial, but not fully part of the state as overflight is allowed. Next 200 miles is the EEZ (Exclusive Economic Zone), where only some rights can be controlled. Oil and fish etc, but they can't control shipping. And the EEZ is settled by neighbour states. Usually the median between baselines of states opposite each other. Baseline being the low water mark on the states land ( but that can be complicated).
This is not directed at your good self of course. For general reading.
So any "blockade" or interdictions will have to be in the EEZ or beyond. Non EEZ sea is the High seas. Act of war to seize a ship in territorial waters. so I reckon the "blockade" will be in the Arabian sea. Probably in the High seas if there is any.
Legally... hmmm. If it is UN sanctioned, then ok. If it is Unilaterally sanctioned by the US, then very grey. There are rules where a vessel can be seized in the high seas, usually for international criminal acts, such as drug smuggling.
Remember the UK has helped the US seize a Russian tanker in the Atlantic. I think it is still held in the Cromarty firth. The crew were sent home. So if sanctioned ok, but I don't think it is 100% black and white.
The US can't just grab the oil though. That would have to be impounded with the ship.
There will be loads of legal papers discussing if the UK seizing the Russian tanker was legal. Must have been "cos Starmer"
I think though, if an Indian Tanker stayed within the 24 miles of Iran, then Pakistan, and into India, the US can't touch it. Not without permission from Pakistan
Not definitive... chewing the cud :-) Need to look up the Russian tanker seizure. I suspect that was on a technicality.