Yahoo! issued a statement saying it continually reviews its business operations to comply with U.S. restrictions on "conducting business in specified countries, such as Iran."

"Consistent with this policy, our current practice is to not accept registrations from countries subject to these restrictions," the company said.

Microsoft had no comment, said The Register, a British Web site covering the online world.

Iran remains an option for Google G-mail users. The company said it did not believe that keeping Iran on its country list violates the sanctions.