DALLAS (Reuters) - U.S.-based airlines reported nonoticeable increase in ticket cancellations Sunday after theUnited States and Britain warned their citizens of an increasedrisk of terror attacks in Europe.

But they also said it was perhaps too early to tell whatthe impact would be of the warnings issued Sunday.

The U.S. State Department put out an alert for Americancitizens traveling in Europe, without singling out any country.The British government updated its travel advice for citizensgoing to France and Germany, raising the terrorism threat levelto "high" from "general."

Delta Air Lines spokesman Carlos Santos, said, "Our flightsare operating their regular schedule, and operations arenormal."

Santos said it was too early to know if customers would becanceling flight plans due to the alert. "I don't want tospeculate on what passengers are going to do. It is hard tosay," he said.

In Dallas-Fort Worth, an American Airlines spokesman saidthe airline had not seen any surge in cancellations related tothe State Department notice.

"We are not seeing much of anything on this at this point,"he said.

Europe is worried about how reports of the threats mightaffect tourism.

The U.S. alert falls short of a more severe one in whichthe State Department may have warned citizens against travelingto Europe. Instead, the alert urges them to take precautionswhen they do travel. (Reporting by Ed Stoddard in Dallas and Carey Gillam in KansasCity; Editing by Jonathan Oatis and Maureen Bavdek)