The United States Department of State/Bureau of Consular Affairs issues Travel Warnings and Travel Alerts. There is a difference between the two; both are important:
Travel Warnings are issued to inform travelers that certain countries/areas have the potential to be unsafe and unsuitable for travel by U.S. citizens. Examples of reasons for issuing a Travel warning might include unstable government, civil war, ongoing intense crime or violence, or frequent terrorist attacks. You need to know the risks of traveling to these places and to strongly consider not going to them at all. Travel Warnings remain in place until the situation changes; some have been in effect for years.
Travel Alerts are issued for short-term events that you should know about when planning to travel to a country. Reasons for issuing a Travel Alert might include an election season that is bound to have many strikes, demonstrations, or disturbances; a health concern such as an outbreak of a contagious disease; or evidence of an elevated risk of terrorist attacks. When these short-term events are deemed to be over, the U.S. Department of State will cancel the Travel Alert.
For more information on Travel Warnings and Travel Alerts, including a current watch list by location, click here.