Several cargo planes have been grounded at separate US airports as authorities investigate suspicious packages, the Transportation Security Administration has said.The investigations are at Newark in New Jersey and Philadelphia.
The planes were taken to remote locations to be searched.
An unconfirmed report by CNN said that a bomb had been discovered on a UPS flight to Chicago from Yemen when it was stopped in London.
CNN said the alert in London centred on an ink toner cartridge converted into a bomb.
It was reported that at least one of the cargo planes being swept was a UPS jet at Philadelphia.
"Out of an abundance of caution the planes were moved to a remote location where they are being met by law enforcement officials," the TSA said.
A UPS courier truck in New York was also being investigated.
But there has been no confirmation as to whether it is linked to the airport checks.
