2 U.S. agencies warn on imminent ISIS attack While the FBI investigates a possible ISIS terror attack on the basis of intercepted chatter and intelligence information, the TSA issued a classified warning that ISIS is planning an attack on U.S. soil. Little is known about the nature of the attack other than its imminence, which has prompted the TSA to deploy its new Visible Intermodal Prevention and Response teams, or VIPR, to various undisclosed locations. The VIPR teams include airports, train stations and other busy transportation hubs.One law enforcement source suggested parts of California were of special concern. As a result of the FBI warning, some cities have increased security as a precaution, but those cities have not been disclosed. The TSA classified warning was issued Friday. The FBI investigation was confirmed Saturday. MORE