Authorities Believe Immediate Threat Contained, But Warn More Attacks Coming

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."

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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.