Oct. 29, 2010 — -- U.S. authorities are cautiously confident that they have contained the imrmediate terror threat by stopping two explosive packages bound for the U.S., but say that Americans should expect more terror attempts from Al Qaeda's Yemen affiliate.
Homeland Security Secretary Janet Napolitano told Good Morning America that "we always presume" more attempts are coming. "We are always leaning forward and thinking about what the next plot could be," said Napolitano, "and how we go after this relentless enemy."
Napolitano also said that the devices intercepted, which originated in Yemen, do bear the "hallmarks of al Qaeda, particularly al Qaeda in the Arabian Peninsula," the terror group's Yemen-based affiliate.
A FedEx package intercepted in Dubai and a UPS package stopped in England were both constructed out of close to a pound of explosive powder hidden inside the toner cartridges of printers. Dubai authorities said Saturday the explosive powder in the FedEx parcel was PETN. PETN is the same material that was used in the failed Christmas day bombing of Northwest flight 253, but the amounts discovered in the devices in Dubai and England were seven or eight times greater.
"The parcel was prepared in a professional way where a closed electrical circuit was connected to a mobile phone SIM card hidden in the printer," said a Dubai police statement. "The tactic carries the hallmarks of methods used previously by terrorist organizations such as al Qaeda."
Based on the initial tip from Saudi intelligence that led to the discovery of the devices in Dubai and England, authorities were searching for additional bombs, but a search of 11 different shipments has turned up no more devices.
Addressing the nation Friday afternoon about what he now calls "a credible terrorist threat against our country," President Obama said the packages from Yemen intercepted in Dubai and England tested positive for explosives.
"Last night and earlier today," said President Obama, "intelligence and law enforcement officials working with our friend and allies identified two suspicious packages bound for the United States, specifically two places of Jewish worship in Chicago."
The president said that he had "directed that we spare no effort in investigating the origins of these suspicious packages and their connection to any additional terrorist plotting."
The initial intelligence report from Saudi intelligence said there could be as many as 15 bomb packages being sent from Yemen to the U.S.
The initial report came late Thursday night and involved two separate packages shipped from Sanaa, Yemen to Chicago, according to law enforcement officials.
Officials said both packages were stopped midway on their trip to Chicago, one at the East Midlands cargo airfield outside London and the other at the airport in Dubai.
Cargo Planes Searched
According to sources, the devices were constructed by gutting a toner cartridge and installing a complete improvised explosive inside it -- a detonator, main charge and cell phone initiator. One source gave an initial estimate that 10 to 14 ounces of homemade high explosive were contained in the devices.
White House spokesman Robert Gibbs said that as a result of the discovery of the packages, "additional measures were taken regarding . . . flights at Newark Liberty and Philadelphia International Airports."
The discovery of the packages led to an international search of cargo planes carrying packages to the United States from Yemen Friday.
Authorities in Newark and Philadelphia searched UPS and FedEx cargo jets. US fighter jets also escorted Emirates Air flight 201 from Dubai into John F. Kennedy airport in New York City Friday afternoon. According to a statement from NORAD, the plane was determined to be "an aircraft of interest."
Gibbs said President Obama was notified of a potential terrorist threat Thursday night by John Brennan, deputy national security advisor for counterterrorism, at 10:35 p.m. "The president directed U.S. intelligence and law enforcement agencies, and the Department of Homeland Security, to take steps to ensure the safety and security of the American people, and to determine whether these threats are a part of any additional terrorist plotting."
The president vowed to enhance screening of cargo planes in the U.S., and said he had been in touch with the president of Yemen.
Brennan issued a statement thanking Saudi Arabia "for their assistance in developing information that helkped underscore the imminence of the threat emanating from Yemen." Brennan also thanked the U.K. and the United Arab Emirates for their assistance.
Further Tests On Package In Britain
Al Qaeda In The Arabian Peninsula
Cargo: 'The Soft Underbelly'
The method of trying to ship the improvised explosives into the country on air cargo flights exposed one of the worst-kept secrets about American security.
At best, only a third of packages coming into the country as air cargo are ever inspected.
"I've called cargo the soft underbelly of aviation security because of the relative little security that is attached to it," said Clark Kent Ervin, former inspector general of the Department of Homeland Security. "I think this just underscores that fact that al Qaeda is always probing for weaknesses in the system and when we close one vulnerability, al Qaeda is just going to find another."
On Friday, Homeland Security agents and intelligence analysts were ordered to go back through previous shipments from Yemen over the last two weeks, as the White House worried that other package bombs might have already made their way into the country.
CLICK HERE to follow ABC News Chief Investigative Correspondent Brian Ross on Twitter.
