The Department of Homeland Security will be advising travelers that security is being tightened at U.S. airports after an attack on Glasgow's airport, reports CBS News correspondent Bob Orr.

Sources tell CBS News that there is no known terror threat facing the U.S., but the airport security upgrades are being made out of an abundance of caution.

White House spokesman Tony Snow said the Transportation Security Administration is implementing "alertness raising packages" at a number of U.S. airports, reports CBS News correspondent Mark Knoller.