Law enforcement officials are investigating suspicious packages in several places in the eastern U.S. and one in England.
Cargo planes in Philadelphia and Newark, N.J., are being swept. The New York Police Department's bomb squad also has stopped a UPS truck on the Queensboro Bridge.
A law enforcement official briefed on the investigation said officials found something suspicious on a cargo plane in Birmingham, England. But test results for explosives were negative. The official spoke on condition of anonymity to discuss the ongoing investigation.
A spokeswoman for Atlanta-based United Parcel Service Inc. said a suspicious package at one of its sites outside London had been turned over to authorities.