In response to the arrests in Britain, U.S. authorities for the first time have invoked the nation's highest terror alert -- level red -- for all flights coming into the United States from the United Kingdom.
They've also tightened security for all U.S. air travel, including banning passengers from carrying any liquids on board. Authorities say they have no indication of any plotting within the United States, but they're taking the steps as a precaution.
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