WASHINGTON — A new terror threat against Europe is not related to the United States, but Americans travelling abroad should take commonsense precautions, the White House said Monday. President Barack Obama's press secretary, Robert Gibbs, emphasized that Americans were not being told to stay home. Obama was briefed on the situation Saturday, Gibbs told reporters. On Sunday, the United States issued an alert to Americans living in or travelling to Europe to be vigilant because of the threat of terrorism there. "We are concerned enough to alert those who are in Europe to be alert to their surroundings," Gibbs said at a White House briefing. People should be alert to suspicious activities and should be aware of where to go in an emergency, he said. Earlier, officials with the FBI and the Homeland Security Department said they had have no indication that terrorists were targeting the United States or its citizens as part of a new threat against Europe. According to an intelligence bulletin obtained by The Associated Press, the FBI and Homeland Security said they believe the al-Qaida terrorist network continues to want to attack the United States, but there is nothing pointing to anything specific, imminent or related to the European plots. They warned law enforcement authorities to be on the lookout for suspicious activity, as it is more difficult to detect terror plots carried out by individuals or small groups. Meanwhile, the national rail system Amtrak will be increasing security beginning Friday for a planned exercise that is not related to the Europe threat, a Homeland Security official said. The official spoke on condition of anonymity to discuss the exercise because it has not begun yet. The exercise, known as operation RAILSAFE, often takes occurs during holidays when rail travel is increased.