General Discussion

from Iran. They are the country that covers the whole north side of the gulf, the straights and part of the Gulf of Oman.
Most navy ships are big and relatively slow and don't maneuver quickly. Cargo ships are worse and unarmed. There is also the possibility of being able to hit ships with 155mm howitzer fire. At the narrowest point of the straight. Those might be hard to hide and move quickly after firing several rounds.

An example is the Russian fleet in the Black Sea. Confined to port by a country with no navy and no air cover.