Emergency personnel work near a grounded UPS cargo jet as the plane is searched by law enforcement officials at Philadelphia International Airport. Image Credit: Reuters

Washington: The United States searched on Saturday for the culprits behind a plot to bomb Jewish targets in Chicago uncovered by the interception in Britain and Dubai of parcels with explosives sent from Yemen.

US President Barack Obama vowed on Friday that US authorities would spare no effort to find the source of the packages, which he called a "credible terrorist threat" aimed at two places of Jewish worship.

Obama said security would be increased for air travel for as long as necessary. US officials said they were searching for more packages that could have come from Yemen, which has become a haven for some anti-American militants.

Radio 2: Explosives found on planes bound for the US. Malak Harb reports

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The security threat unsettled Americans just days before they vote in midterm congressional elections that have been dominated by economic woes rather than the issue of terrorism.

Suspicion fell on Al Qaida in the Arabian Peninsula, which operates out of Yemen and claimed responsibility for a failed plot to blow up a US plane over Detroit on Christmas Day in 2009.

"Initial examinations of those packages has determined that they do apparently contain explosive material," Obama said at a press briefing at the White House.

Same chemical used in underwear bomb plot

The New York Times reported that the packages contained PETN, the same chemical explosive used in the bomb sewn into the underwear of the Nigerian man who attempted to blow up an airliner over Detroit at Christmas, a plot hatched in Yemen.

The newspaper cited Representative Jane Harman, a Democrat on the House Homeland Security Committee, who was briefed by the Transportation Security Administration.

The improvised devices contained computer printer cartridges filled with the explosive, but one used a cell phone as a detonator and the other had a timer, she told the Times.

US law enforcement officials would not confirm the report, saying tests were still being done on the explosives.

The White House said "both of these packages originated from Yemen" and Obama was informed of the threat on Thursday.

One of the packages was found on a United Parcel Service cargo plane at East Midlands Airport, north of London. The other was discovered at a FedEx Corp facility in Dubai.

UPS and FedEx, the world's largest cargo airline, said they were halting shipments from Yemen. UPS planes were searched and then cleared in New Jersey and Philadelphia.

One US official and some analysts speculated that the parcels may have been a test of cargo screening procedures and the reaction of security officials. "This may be a trial run," the US official said.

The White House said Saudi Arabia helped identify the threat from Yemen, while Britain and the United Arab Emirates also provided information.

Obama's counterterrorism adviser, John Brennan, would not say how the United States learned of the plot. But he told reporters: "We were onto this. We were looking for packages that were of concern."

Of the plotters, Brennan said: "Clearly they are looking to identify vulnerabilities in our system. We've been able to stay ahead of them."

Britain launches probe

In London, British authorities are probing whether a package from Yemen containing explosives found on a cargo jet bound for the United States was a "viable" bomb, Home Secretary Theresa May said on Saturday.

"At this stage I can say that the device did contain explosive material. But it is not yet clear that it was a viable explosive device. The forensic work continues," May said.

Britain is "urgently considering" new security measures for air cargo from Yemen following the discovery of the package and is "in discussion with industry contacts" over the issue, May said.

Yemen to cooperate


For its part, the Yemeni government expressed astonishment at reports linking it to the packages but said in a statement it was cooperating with the US and international investigations.

The statement warned against "rush decisions in a case as sensitive as this one and before investigations reveal the truth."

UAE statement

“A suspicious looking package was found on Friday coming from Yemen. The package was to be sent to the US via a Fed Ex airplane,” said a press release issued by the UAE General Civil Aviation Authority, reported WAM.

Authorities sent the package to the lab for further investigations. There was also a complete cooperation with the civil aviation authorities in Yemen, the US and the UK, the statement said.

The Emirates flight to NY didn't carry any package that came from Yemen, WAM adds quoting an Emirati official.

The UAE is keen to apply the highest standards of security in its airports to safeguard the safety and security of passengers and cargo. The airports in the country have been supplied with the best equipment to scan both passengers and cargo before boarding flights.

Further details will be revealed later, added the press release.

Investigation

Authorities were investigating reports the parcels were bound for a synagogue and Jewish community centre 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 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."

The US Department of Homeland Security said it was increasing aviation security measures as a result of the scare.

The Yemeni embassy in Washington said "the Yemeni government launched a full-scale investigation. We are working closely with international partners - including the US - on the incident."

Yemen has been trying to quell a resurgent branch of Al Qaida, which has stepped up attacks on Western and government targets in the Arabian Peninsula country.