Icann's chief Paul Twomey said the decision was not political.
"The heart of the decision today was not driven by a political consideration," he told the Associated Press news agency.
The idea for an .xxx domain was first suggested in 2001 but plans for it have been heavily criticised by many people and organisations, including former Icann board member Karl Auerbach and American conservative religious groups, such as the Family Research Council.
ICM Registry, the company that came up with the idea and planned to run the .xxx, said the domain would have made it much easier to find and filter pornography online.
But critics claimed that because signing up for .xxx was on a voluntary basis, there was no guarantee pornographers would move material to the new domain.
