Two suspicious packages being flown from Yemen to the United States were found in Britain and Dubai today after a tip prompted authorities to search cargo planes on both sides of the Atlantic.
"Both of these packages originated from Yemen," White House spokesman Robert Gibbs said in a statement, adding that president Barack Obama "was notified of a potential terrorist threat on Thursday night".
Speaking to reporters, Mr Obama described the alert as a "credible terrorist threat" against the US. He said Yemen's president had pledged "full support" in the investigation.
Authorities were investigating reports the parcels were bound for a synagogue and Jewish community center in Chicago.
Citing law enforcement sources, the Anti-Defamation League said there was a threat to US Jewish institutions from packages mailed from Britain, Yemen and Saudi Arabia.
One of the suspicious packages was found on a United Parcel Service cargo plane at East Midlands Airport, about 160 miles (260 km) north of London. The other was discovered at a FedEx Corp facility in Dubai.
"As an additional safety measure, FedEx has embargoed all shipments originating from Yemen," said Maury Lane, a spokesman for the world's largest cargo airline. "The package never was on a FedEx aircraft. We don't fly to Yemen."
British police said an item found on the UPS plane was sent for further testing. CNN said it was an ink toner cartridge converted into a bomb but an FBI source told Reuters that initial tests in Britain revealed no explosives.
The BBC and Sky News quoted unidentified sources as saying the item was not a bomb but still was "potentially sinister".
In the United States, UPS planes were checked in New Jersey and Philadelphia. The Transportation Security Administration said they were searched "out of an abundance of caution".
If a link to militants was found after the discoveries today, al Qaeda in the Arabian Peninsula would top the list of suspects, a US official told Reuters.
AQAP and one of its leading figures, American-born Muslim cleric Anwar al-Awlaki, have become priority US targets since the group took responsibility for a failed plot to blow up a US passenger jet on Christmas Day in 2009.
One US official and some analysts speculated that the suspicious parcels may have been a test of cargo screening procedures and the reaction of security officials.
"One possibility, if this is terrorism related, is that this may be a trial run," the US official said.
Intelligence about the possible plot had come from an ally abroad, the official said, without elaborating.
In another sign of concern over the threat, US officials said fighter jets escorted an Emirates flight arriving from Dubai into New York's John F. Kennedy International Airport as a precaution because it was carrying cargo from Yemen.
"There is no known threat associated with this cargo or this flight," said FBI spokesman Richard Kolko.
A Pentagon spokesman said two Canadian CF-18 jets tracked the Emirates plane as it flew through Canadian airspace, before handing off to two US F-15s that escorted it to New York.
The US Department of Homeland Security said it was increasing aviation security measures as a result of the scare. The British government said it was "too soon to say" whether it would follow suit but was "urgently considering" what steps to take about freight coming from Yemen.
The Yemeni embassy in Washington said there were no direct flights from Yemen to Britain or the United States, adding that no UPS cargo flights land or take off from Yemeni airports.
"As of now, we have no confirmation on the content of the suspicious package(s)," said Mohammed Albasha, an embassy spokesman. "The Yemeni government launched a full-scale investigation. We are working closely with international partners - including the US - on the incident."
The man accused of the failed Christmas Day bombing, Umar Farouk Abdulmutallab, has told US investigators he received the explosive device and training from al Qaeda militants in Yemen.
Yemen has been trying to quell a resurgent branch of al Qaeda, which has stepped up attacks on Western and government targets in the Arabian Peninsula country.
Reuters