Iran: what the law of the sea says about detaining foreign ships in transit

With Stena Impero now detained in an Iranian port, under investigation for its alleged transgression against navigation regulations in the Strait of Hormuz, there are several legally curious aspects to this affair, of which those rules are just one aspect.

So far the Iranian authorities have given only scantdetail of what the unlawful actions of the UK-flagged ship were that caused them to detain it and the information seems contradictory: some reports say the ship collided with a fishing vessel, others that the change of course ordered by the Revolutionary Guard vessel was for security reasons, but both are wanting as pretexts for interfering with merchant shipping in straits used for international navigation.