Suspicious packages discovered in Dubai and England in air cargo shipments to the U.S. contained explosive materials and appeared headed for Jewish places of worship in Chicago, President Obama confirmed Thursday afternoon.
Obama's remarks in a brief address to reporters capped a tense daylong drama, in which federal authorities grounded UPS planes at airports in Newark, N.J., and Philadelphia to inspect packages based on fears of a terrorist threat originating from Yemen.
The Yemen-based Al Qaeda in the Arabian Peninsula is suspected, and U.S. officials told the Associated Press that the chemical used, PETN, was also used in the failed Christmas Day airline bombing that was tied to the same group.
President Obama, confirming that authorities had uncovered a "credible terrorist threat," spoke shortly after military jets escorted a passenger jet from the United Arab Emirates to New York's JFK airport as a precautionary measure because it was carrying a package from Yemen.
"We will continue to pursue additional protective measures for as long as it takes to ensure the safety and security of our citizens," Obama said.
A UAE official told the Associated Press late Friday that an "explosive device" in Dubai was found in a courier company's regional hub, though it was reported that no explosives were found on board the flight that landed in JFK.
Later Friday night, JFK authorities also investigated a British Airways jetliner arriving from London. A spokeswoman for the airline did not say why Flight 115 was targeted or if the jet was carrying any cargo from Yemen, the Associated Press reported.
FedEx reported earlier that a suspicious package was found at its Dubai facility.
Another package, found on a UPS plane at East Midlands Airport in central England, contained what looked like a toner cartridge with white powder and wires coming out of it.
The Thursday night discoveries prompted U.S. authorities on Friday to sweep a UPS plane in Newark, N.J., two UPS planes in Philadelphia and two UPS trucks in New York City.
The planes in Philadelphia are still being investigated. The Newark flight and New York trucks have been cleared.
White House Press Secretary Robert Gibbs said President Obama was alerted Thursday night, and administration officials have been monitoring the situation.
"Based on close cooperation among U.S. government agencies and with our foreign allies and partners, authorities were able to identify and examine two suspicious packages, one in London and one in Dubai. Both of these packages originated from Yemen," Gibbs said in a written statement. "As a result of security precautions triggered by this threat, the additional measures were taken regarding the flights at Newark Liberty and Philadelphia International Airports.
Given the origin of the packages, Al Qaeda in the Arabian Peninsula "is at the top of the list" of suspects, a U.S. official told Fox News.
"Since two of the suspicious packages that were intercepted were addressed to religious institutions in Chicago, all churches, synagogues and mosques in the Chicago area should be vigilant for any unsolicited or unexpected packages, especially those originating from overseas locations," Chicago FBI spokesman Ross Rice said.
Federal law enforcement officials said the suspicious device that resembled a toner cartridge was removed from the a flight in a distribution center at East Midlands Airport in the U.K.
A crew member aboard a UPS plane arriving to Philadelphia from Paris later notified authorities on approach about a suspicious package. The crew member described a possible radiological component to the package, the incident report said. The two occupants safely exited the aircraft after landing in a remote area of the airport.
A second UPS plane was isolated near the UPS terminal at the Philadelphia airport before take off, the report said.
A third UPS plane, which arrived at Newark Liberty Airport from East Midlands in the U.K., was investigated, but UPS says it was cleared and proceeded on to Louisville, KY.
Two UPS trucks in Brooklyn and Queens, N.Y., were also investigated and cleared, officials said.
Law enforcement officials also are investigating a suspicious package in Portland, Maine. No word on whether that package has any links to UPS or Yemen.
"As an additional safety measure, FedEx embargoed all shipments originating from Yemen," Maury Lane, spokesman for FedEx told Reuters.
FoxNews.com's Diane Macedo contributed to this report.