Authorities Believe Immediate Threat Contained, But Warn More Attacks Coming

This undated photo released by the Dubai Police via the state Emirates News Agency (WAM) on...

This undated photo released by the Dubai Police via the state Emirates News Agency (WAM) on Saturday, Oct. 30, 2010, claims to show parts of a computer printer with explosives loaded into its toner cartridge found in a package onboard a cargo plane coming from Yemen, in Dubai, United Arab Emirates. 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.

(Dubai Police via Emirates News Agency/AP Photo)
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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.

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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.