The agency that regulates web addresses has rejected, for the third time, a proposal to give adult websites their own top-level domain. The plan, which has been under discussion for several years, would have involved pornographic sites moving from .com or .co.uk sites to addresses ending in .xxx.

Religious groups, along with many in the adult-entertainment industry, had criticised the plan. This week the Canadian government also warned the Internet Corporation for Assigned Names and Numbers that if it approved the plan it would have to start regulating content.

Supporters of the idea argued that adult sites could be better regulated if they were kept within their own domain. They also said that web users would be less likely to encounter pornographic material accidentally and that parental filters could recognise unsuitable sites more easily.

Opponents within the porn industry were concerned that the proposal, while billed as voluntary, would later become compulsory and would confine adult content to a ghetto. Religious groups said that the .xxx domain would legitimise pornography.

The proposal was defeated this morning by nine votes to five, with one abstention. It was the third time the Icann board had rejected to idea since it was suggested nearly seven years ago by ICM Registry.

“We are extremely disappointed by the board’s action today,” Stuart Lawley, ICM’s president and chief executive, said. He added that the organisation would continue to fight for the establishment of a .xxx domain.