Americans are warned to be aware of their surroundings and protect themselves when traveling, especially when they are in public places like tourist sites, airports or when they are using public transportation.
The alert does not warn U.S. citizens against travel to Europe.
Britain's Home Office has not raised its threat level. A statement released Sunday confirms that British authorities are keeping their threat level at "'severe," which means than an attack is highly likely.
But, the UK's Foreign and Commonwealth Office (FCO) has changed its travel advisory for British citizens in France and Germany from a "substantial" threat of terrorism to a "high" threat. The FCO said it does not comment on intelligence matters and thus can't specify whether the change is related to the U.S. travel alert.
Germany's interior ministry said in a statement that the warning for Americans comes in light of recent threats and that Berlin was informed by the U.S. of the decision to issue the alert. Germany will analyze and evaluate the intelligence data coming in but will not be changing its current threat level at this time, according to the statement.