The Obama administration will warn U.S. citizens to be vigilant as they travel in Europe, providing updated guidance prompted by al-Qaida threats, American and European officials told. Such a move could have negative implications for European tourism, business and diplomacy if travelers fear there's a possibility of terror attacks.The State Department will issue a "travel alert" for Europe on Sunday morning that advises Americans to stay vigilant on the continent because of threat information, senior U.S. officials told. The officials spoke on condition of anonymity because a final decision has not been announced. "This travel alert is a cumulative result of information we have received over an extended period," one senior administration official said. "We are constantly monitoring a range of threat streams and have monitored this and others for some time."State Department spokesman P.J. Crowley declined to comment on the matter. But he said the administration remains focused on al-Qaida threats to U.S. interests and will take appropriate steps to protect Americans. A European official briefed on the talks said the language in the U.S. alert is expected to be vague. It won't address a specific country or specific landmarks, the official said. European and U.S. officials have not identified any specific targets that terrorists might be considering, the official said.