Travellers in the following categories are no longer eligible to travel or be admitted to the United States under the Visa Waiver Programme (VWP) using an Electronic System for Travel Authorisation (ESTA).
• Nationals of Visa Waiver Programme (VWP) countries who have travelled to or been present in Iran, Iraq, Sudan, or Syria on or after March 1, 2011 (with limited exceptions).
• Nationals of VWP countries who are also nationals of Iran, Iraq, Sudan, or Syria.
In addition, all travellers from VWP countries must use an electronic passport for travel to the United States by 1 April 2016.
For more information, please visit the U.S. Customs and Border Protection site