President Trump signed an executive order today which bans foreigners from certain countries from entering the US for at least 90 days. This applies to citizens from Iraq, Syria, Iran, Libya, Somalia, Sudan and Yemen. Effective immediately, citizens of these countries may not enter the US even though they may have a valid immigrant or nonimmigrant visa.
Click here to read the full text of the order http://www.npr.org/2017/01/31/512439121/trumps-executive-order-on-immigration-annotated