On Friday, January 27, 2017, President Donald Trump signed an Executive Order titled “Protecting the Nation from Foreign Terrorist Entry into the United States”. This Executive Order had the effect of banning nationals of Iraq, Syria, Sudan, Iran, Somalia, Libya, or Yemen from entering the United States for a period of at least 90 days (potentially longer). This travel ban includes foreign nationals who have dual citizenship with one of the listed countries as well as another foreign country not on the list. U.S. Lawful Permanent Residents (green card holders) are exempt from the travel ban subject to successful national security checks as their entry has been determined to be in the national interest.
Citizens of any of the seven countries listed in the Executive Order should avoid departing the United States for at least the next 90 days (possibly longer). In addition, any foreign nationals who have traveled to any of the above countries should expect delays in reentering the United States due to enhanced security vetting.
For additional information, please see
https://www.dhs.gov/news/2017/01/29/protecting-nation-foreign-terrorist-entry-united-states.