Washington ? The White House says President Barack Obama was notified about a potential terrorist threat after suspicious packages were discovered aboard two airplanes bound for the U.S.

No explosives have been found. A U.S. official says authorities are investigating whether the packages may be a dry run for a plot to send bombs through the mail.

A suspicious package containing a toner cartridge with wires and powder was found during routine screening of cargo in the United Kingdom, prompting authorities to scour three planes and a truck in the United States on Friday.

Searches were conducted in Philadelphia, Newark, N.J., and New York City. All the packages believed to be suspicious came from Yemen and were being sent via UPS.

Yemen is the home of the al-Qaida branch that claimed responsibility for an attempted bombing of a U.S.-bound airliner on Christmas.