"The heart of the decision today was not driven by a political consideration," Paul Twomey told the Associated Press news agency.

The idea for an .xxx domain was first floated in 2001.

A final decision on approving the exclusive porn domain has been delayed several times - most recently in December.

In August, the decision was postponed following a request from the US Department of Commerce which had "concerns" about the domain.

Plans for the .xxx have been criticised by many people and organisations, among them former Icann board member Karl Auerbach and US conservative religious groups, including the Family Research Council.

ICM Registry, the company that proposed and plans to run the .xxx, said the domain would have made it easier to find and filter pornographic material online.

Critics said that because signing up for .xxx was voluntary, there was no guarantee pornographers would move material to the new domain, not least because many have established themselves on other well-known sites.