The Obama administration will announce as early as Thursday its plan to introduce new visa requirements for European travelers who are dual nationals of Iran, Iraq, Sudan or Syria, or who have visited any of these countries in the last five years.

U.S. officials and congressional aides involved in discussions say the Homeland Security Department will outline how it will phase in the new rule, designed to make it harder for Europeans who have fought for the Islamic State to enter the United States.

Iraq and Syria were targeted because the Islamic State has seized significant territory in each country. Iran and Sudan, like Syria, are designated by the U.S. as state sponsors of terrorism.

The officials and aides weren't authorized to speak publicly on the matter and demanded anonymity.