The U.S. Department of Homeland Security raised threat levels for commercial flights and is "expanding the intensity of existing security requirements

" following the arrest by British authorities of "a significant number of extremists engaged in a substantial plot to destroy multiple passenger aircraft flying from the United Kingdom to the United States," according to a DHS statement. For flights originating in the United Kingdom bound for the United States, the threat level is now "severe." For all other flights operating in or destined for the United States, the threat level is now "high." As a result, passengers cannot carry "any liquids, including beverages, hair gels, and lotions" onto airplanes (baby formula and medicine are excluded from the ban), and should expect "additional" security measures. The Air Transport Association said U.S. carriers were cooperating with the new "temporary" DHS policies. Meanwhile, several European carriers warned passengers of lengthy delays and cancellations for today's flights to, from and through U.K. airports.