DUBAI // Yemeni security forces last night arrested a woman suspected of sending two intercepted bombs, including the one found on a FedEx cargo plane in Dubai on Friday.
Meanwhile the British prime minister, David Cameron, said he believed the second device, found on a plane at East Midlands Airport in England on the same day, could have been intended to go off in flight.
Both parcels originated in Yemen and were addressed to synagogues in the Chicago area in the United States. Dubai's chief of police has voiced frustration that the package intercepted there had passed through air security in Yemen and Qatar undetected.
The Yemeni woman, who has not been identified, was arrested after police surrounded her house in the republic's capital, Sana'a.
Security officials said she had been detained as part of the search for a number of suspects believed to have used forged documents and ID cards in order to mail the packages.
They said the suspects were believed to be linked to the al Qa'eda faction in Yemen. Dubai Police concurred, saying the plot "carries features similar to previous attacks carried out by terrorist organisations like al Qa'eda".
Earlier, Yemeni security forces closed the offices of FedEx and UPS on the orders of the attorney general, according to the country's defence ministry. Witnesses said they stormed the offices and seized a number of packages. A security official said police there were investigating "about 24" more packages.
"This does not mean these packages contain explosive materials, but they are suspicious," the official said. "Police have been interrogating some employees at the airport and the parcel companies in connection with the two suspicious packages."
The devices were both hidden inside printers. The one found in Dubai was described as a sophisticated device containing plastic explosives and a mobile-phone detonator.
Dubai Police said two highly explosive substances, PETN and lead azide, were "professionally loaded" into the printer's toner cartridge. The material was connected through an electric circuit to a mobile phone chip.
The device intercepted in Dubai was discovered after a telephone tip-off and successfully defused. US intelligence officials have said the package was discovered based on intelligence picked up by Saudi Arabia. The White House said the US president, Barack Obama, had phoned King Abdullah to thank him for the "critical role" of Saudi counter-terrorism authorities in uncovering the plot. The General Civil Aviation Authority, the UAE's aviation regulator, confirmed last night that the package had been shipped from Sana'a on a Qatar Airways plane to Doha, and then to Dubai.
"How did this parcel get through both the freight company as well as security companies in both countries?" asked Lieutenant General Dahi Khalfan Tamim, the Dubai Police chief. Officials at Dubai International Airport said full safety measures were in place. "We always follow international standards, we use the latest technology. Whatever needs to be done in the future also we will do it," said Jamal al Hai, Dubai Airports senior vice president.
President Obama's counterterrorism adviser, John Brennan, has called Yemen's president, Ali Abdullah Saleh, to offer America's help in the fight against al Qa'eda.
However, Mr Saleh said he would not accept any foreign military intervention against al Qa'eda. "We will not accept any intervention in our internal affairs," he said. "We do not want anybody to hunt down al Qa'eda for we will chase down al Qa'eda [militants] wherever they are…. But we will be grateful to anyone who will provide us with information." PETN is the short name for the plastic explosive pentaerythritol tetranitrate.
David Learmount, operations and safety editor of Flightglobal, a British-based aerospace bulletin, said PETN was the substance used by the Unabomber, Theodore Kaczynski. He is serving a life sentence for a series of attacks in the US between 1978 and 1995 that killed three people and injured 23. Kaczynski posted or hand-delivered his bombs.
One device in a parcel in the hold of an American Airlines flight in November 1979 resulted in a dozen minor injuries due to smoke inhalation. Mr Learmount cautioned that vigilance was essential, more so than security upgrades. "All security depends on a series of checks," he said. "All it requires is that existing procedures are rigorously enforced."
The first level involves checking the person who sends a package. "The freight forwarder has to check this before the package even reaches the airport, before it even reaches the airline," Mr Learmount said. "What do I know about the person sending it? Is that person on a security list of any country, what about the country sending, transiting and receiving the package? Are those on any list?"
Only after the first level of checks is complete is the package scanned at the airport, he said.
Theodore Karasik, the director of research and development at the Institute for Near East and Gulf Military Analysis in Dubai, said UAE authorities must stay one step ahead of al Qa'eda. "We need to think about how they will try to bypass systems and equipment in place," he said. "I think what needs to be done now is to understand how al Qa'eda in the Arabian Peninsula will continue to try to get a weapon onto an aircraft, and have the appropriate equipment in place to pre-empt it." Mr Karasik said renewed intelligence was crucial to understanding how explosives could be shipped on carriers.
"A lot more intelligence will be needed," he said.
"Saudi intelligence has come out terrifically. They have infiltrated parts of the group [al Qa'eda], they will continue to have this access and maybe they will find out how they plan to modify these devices."
* With additional reporting by Mohammed al Qadhi from Sana'a, Eugene Harnan, Zoi Constantine, Megan Detrie and agencies