URN in its basic form is not HTTP URI, but it can easily be expressed as HTTP URI as long as that is the only way of making the URN actionable. All persistent identifiers are used in this manner for the time being.
For instance, the URN of the National Library of Finland is
As HTTP URI it becomes actionable
This URL is protocol dependent and therefore not nearly as persistent as the URN. If and when URN Global resolver discovery service is in place, URNs may become actionable without the protocol dependent extension, provided that the URN namespace specific string contains a “hint” which makes it possible to find the right URN resolver. All URNs the national library of Finland has assigned are like that.
Anyone planning to use IRIs should be cautious because the standardization status of IRIs is confused. The IETF concluded that RFC 3987 is inadequate and established a working group the revise the RFC, but the WG could not reach consensus on how to revise the specification and gave up.
The problems with IRIs are related to, among other things, security, internationalization and weaknesses in the URI specification (RFC 3986).