An official from President George Bush's administration has asked for the brakes be put on the planned domain name until its impact is studied more.

The domain was given the go-ahead by Icann (Internet Corporation for Assigned Names and Numbers) in June.

But some are concerned that it would encourage more porn on the net.

The domain name was expected to get final approval by the net's supervisory body, Icann (Internet Corporation for Assigned Names and Numbers), on Tuesday.

Net domains such as .com. and org. are overseen by Icann. It polices the companies that run the different domains and approves the expansion of the different net names that can be bought and used.

The ICM Registry, the not-for-profit group which would operate the .xxx domain name, said it would agree to a month's delay in order to explore some of the concerns which have been voiced.

Easy filter?

The .xxx domain name was approved five years after it was first proposed.

The idea is that sexually-explicit sites will move to the new domains to make it easier for people to filter and avoid them.

In a statement, the ICM Registry which originally proposed the idea said it would "help protect children from exposure to online pornography and also have a positive impact on online adult entertainment through voluntary efforts of the industry".

But some are sceptical that it will allow for more controls over sexually-explicit content.

"The Department of Commerce has received nearly 6,000 letters and e-mails from individuals expressing concern about the impact of pornography on families and children," said Mr Michael Gallagher, assistant secretary at the US Commerce Department, in a letter.

There has been growing opposition to the new domain name. In June, concern was expressed by net privacy campaigners who said it could provoke censorship problems for years.

Last week, a letter from Mohamed Sharil Tarmizi, chairman of Icann's Government Advisory Committee, reiterated the concern that several countries had over the decision.

It requested that Icann "allow time for additional governmental and public policy concerns to be expressed before reaching a final decision" on the registration of the domain name.

More than 10% of all online traffic and 25% of all global net searches are for adult content, according to the ICM Registry