This is the first time that the red alert the highest level in the Homeland Security Warning system-- has been invoked. It designates a "severe risk of terrorist attacks."
The alert for all flights coming or going from the United States was also raised.
"We believe that these arrests (in London) have significantly disrupted the threat, but we cannot be sure that the threat has been entirely eliminated or the plot completely thwarted," Homeland Security Secretary Michael Chertoff was quoted as saying.
"To defend further against any remaining
The plan involved airline passengers hiding masked explosives in carry on luggage, another official was quoted as saying. "They were not yet sitting on an airplane," but were very close to traveling.
"Due to the nature of the threat revealed by this investigation, we are prohibiting any liquids, including beverages, hair gels, and lotions from being carried on the airplane," Chetroff said, warning that air travelers within in the US too "should also anticipate additional security measures within the airport and at screening checkpoints."