British police said in a statement Wednesday that forensic evidence shows the device, originally sent from Yemen, could have been activated over the Eastern Seaboard had it not been removed from a cargo plane in the U.K.
British investigators said Wednesday that a mail bomb intercepted last month at an English airport could have been detonated over the U.S. East Coast.
In a statement, Scotland Yard said forensic evidence shows the device -- originally sent from Yemen by way of Cologne, Germany -- was set to activate at time when the flight it was on would have been over U.S. territory.
"Forensic examination has indicated that if the device had activated it would have been at 10:30 hrs BST [British Summer Time] on Friday, 29 October 2010," the statement read. "If the device had not been removed from the aircraft the activation could have occurred over the eastern seaboard of the U.S."
Both U.S. and British authorities have said that they only narrowly thwarted a plot in which Yemeni terrorists hid two powerful bombs -- each containing the plastic explosive PETN -- inside printer cartridges and shipped them to addresses in Chicago.
One bomb was intercepted at central England's East Midlands Airport, and the other was discovered at a FedEx cargo facility in Dubai.
Authorities initially thought the packages were intended to explode when they reached the destinations on the addresses -- Chicago synagogues -- but officials say the timing would have detonated them well before then.
In Washington on Wednesday, White House spokesman Nicholas Shapiro thanked British officials for their efforts, calling them "highly professional."
He praised the efforts of intelligence and law enforcement professionals in the U.K., the United Arab Emirates, Saudi Arabia and the United States. Authorities will continue to work together "to address and counter the threat posed by al-Qaida in the Arabian Peninsula," Shapiro said.
In a related development, the FBI and Homeland Security said Wednesday that al-Qaida's affiliate in Yemen, known as al-Qaida in the Arabian Peninsula, or AQAP, was not behind the Sept. 3 crash of a UPS cargo plane in Dubai. That crash came nearly a month before the discovery of the parcel bombs.
According to a copy of an FBI bulletin sent to law enforcement agencies, AQAP's "assertion of responsibility for the 3 September 2010 crash of a UPS cargo plane in Dubai is false."
"Other terrorist organizations have falsely claimed credit for events with a high media profile to bolster their image and external perceptions of their operational capabilities," the bulletin read.
The Yemen-based terrorist faction had claimed responsibility last week for both the cargo plane crash and the recent mail bomb plot.
In its statement, AQAP said that it "downed the UPS airplane but because the enemy's media did not attribute the act to us, we kept silent about the operation until we could return the ball once more."
Authorities in the U.S. and the United Arab Emirates have found no evidence of an explosion aboard the UPS cargo plane. They have said the UPS plane crashed shortly after takeoff because of an onboard fire.
Investigators have taken a second look at the incident in the wake of the parcel bomb plot but found nothing so far to alter their earlier conclusion that the crash was an accident.
NPR's Philip Reeves reported from London for this story, which contains material from The Associated Press. Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/.