The British did this to enforce sanctions against Syria
Sanctions that Iran did not sign on to. So are you saying it's more of a blockade? Which is an act of war. So if Russia unilaterally announced sanctions against Israel, then sent warships to the Med to forcefully intercept tankers, that would be fine and legal?
Of course, you can call the EU aggressors against Syria and Iran... if you're on the wrong side of history.
Low IQ Well Poisoning. If anything Iran is on the "right side of History" against Saudi Arabia and the Sunni Bloc.
If Russia did this and then sent warships to the Med to intercept tankers, it'd be an act of war. If Russia did this and then intercepted a Polish tanker in Kaliningrad to enforce their sanctions, it'd be within their right, though I'd find it regrettable because my government isn't gassing its own people and isn't targeting innocents with slaughter.
And Iran isn't on the right side of history of anything. Saying this is atrocious- they started the war in Yemen that took so many lives, they're trying to increase their influence across the Middle East by causing instability and civil wars and supporting terrorism. The fact that the Saudis aren't on the right side of history either doesn't make Iran any better. Foreign relations aren't done in a complete moral vaccum- at some point, you need to shed the cynicism and understand when one side is evil, and its actions should be treated as such.