A bomb found on a US-bound cargo plane was powerful enough to bring down an aircraft, British authorities said on Saturday, as forces in Yemen searched for suspected al Qaeda militants behind a plot involving Jewish targets in Chicago.
"I can confirm the device was viable and could have exploded. The target may have been an aircraft and had it detonated the aircraft could have been brought down," British Home Secretary Theresa May said.
Two parcels containing explosives -- addressed to synagogues in Chicago and sent from Yemen -- were intercepted in Dubai and Britain on Friday, following an intelligence tipoff that triggered a massive international response.
Officials said the parcel bombs had the hallmarks of al Qaeda, and in particular al Qaeda in the Arabian Peninsula, and at least one of them included the same explosives used in a failed attempt to blow up a US jet on Christmas Day last year.
In Washington, US Homeland Security Secretary Janet Napolitano said authorities were checking whether other packages had been sent before the two that were intercepted.
"We're doing some reverse engineering as it were to identify other packages from Yemen," she said on NBC News.
President Barack Obama on Friday said US authorities would spare no effort to find the source of the packages which he called a "credible terrorist threat" aimed at two synagogues in his home town of Chicago.
Obama called Saudi King Abdullah and British Prime Minister David Cameron on Saturday to discuss the parcel bomb plot, the White House said.
The White House said Saudi Arabia had helped to identify the threat from Yemen while Britain and the United Arab Emirates also provided information.
One of the packages was found on a UPS cargo plane at East Midlands Airport, about 160 miles (260 km) north of London. The other was discovered at a FedEx facility in Dubai.
UPS and FedEx halted shipments from Yemen and on Saturday Yemen shut down both companies' operations there, citing security concerns.
HIDDEN IN A PRINTER
Dubai police, who defused the device, said the explosive was hidden in a printer cartridge and expertly linked a closed electrical circuit to "a mobile phone SIM card hidden inside."
Britain said it will immediately halt all air freight from Yemen into or through Britain. Direct cargo and passenger flights from Yemen to Britain were suspended in January after a failed plot last year to blow up a US jet bound for Detroit with explosives a Nigerian man hid in his underwear.
The latest plot originating in Yemen further heightened security concerns about the unstable Arab country, seen by the West as the home of al Qaeda's most inventive and audacious affiliate.
Al Qaeda in the Arabian Peninsula, or AQAP, and one of its leading figures, US-born Muslim cleric Anwar al-Awlak, have been priority US targets since it took responsibility for the Christmas Day 2009 attempted bombing.
Dubai police said they found pentaerythritol trinitrate, or PETN, in the printer cartridge, the same chemical explosive used in that failed plot.
There was no immediate claim or responsibility for the parcels, but US officials suspect AQAP.
In Yemen, dozens of heavily armed police and military forces were scattered across the Yemeni capital Sanaa, including the diplomatic quarter and the large ring road around the city, stopping cars and questioning passengers.
Yemen had also stepped up security at its air and sea ports, a security official said, although a witness on Saturday reported no visible extra security measures.
Obama on Friday said security would be increased for American air travel for as long as necessary.
The US president went ahead with a weekend campaign trip in four states to rally his fellow struggling Democrats before Tuesday's US congressional elections.
The package scare caused broad disruptions on Friday, with the US scrambling fighter jets to accompany a passenger jet and using explosive experts to search cargo planes. UPS planes were searched and then cleared in New Jersey and Philadelphia.
