The U.S. State Department issued an alert on Sunday urging Americans traveling to Europe to be vigilant about possible terrorist attacks in a statement that specifically cites the potential involvement of Al Qaida. The British government, meanwhile, raised the threat of terrorism to "high" from "general" for Britons in France and Germany.

The decisions to caution travelers came as counterterrorism officials in Europe and the United States are assessing intelligence about possible plots originating in Pakistan and North Africa aimed at Britain, France and Germany.

The U.S. travel alert urges extra caution and does not discourage Americans from visiting Europe. An American official who confirmed the warning on Saturday, who did not want to be identified speaking about internal government deliberations, said a stronger “travel warning” that might advise Americans not to visit Europe was not under consideration. European officials have been concerned about the impact on tourism and student travel from any official guidance to American travelers.

"Current information suggests that Al Qaida and affiliated organizations continue to plan terrorist attacks. European governments have taken action to guard against a terrorist attack," according to the State Department statement.