U.S. intelligence officials now consider Ibrahim Hassan al-Asiri the chief suspect behind the mail bombs bound for the United States from Yemen.

He is the same man who is suspected of packing explosives into the underwear of a Nigerian man who tried to blow up a Detroit-bound airliner last Christmas.

Yemeni security officials said they are searching for al-Asiri, who is believed to be in Marib province.

Yemeni authorities have taken several people into custody for questioning, including a computer engineering student who was later released. A Yemeni official said on Sunday authorities no longer believe the 22-year-old student mailed the bombs, but that someone might have used her identity.

One of two bombs mailed from Yemen and intended for Chicago-area synagogues travelled on passenger flights within the Middle East, a Qatar Airways spokesman said earlier Sunday.

The U.S. said the plot bears the hallmarks of al-Qaeda's offshoot in Yemen, and it has vowed to destroy the group.

FedEx and UPS have suspended shipments out of Yemen. One of two mail bombs thought to have originated there was sent via UPS but intercepted in Britain. (Erik S. Lesser/Associated Press)

The airline spokesman said a package containing explosives hidden in a printer cartridge arrived at Qatar Airways's hub in the Qatari capital, Doha, on a flight from Yemen — an Airbus A320 that can carry up to 144 passengers.

It was then shipped on a separate Qatar Airways plane to Dubai in the United Arab Emirates, where it was discovered by authorities late Thursday or early Friday. A second, similar package turned up in England on Friday.

The airline spokesman disclosed the information on condition of anonymity, in line with the company's standing policies on conversations with the media.

The plot was the latest to expose security gaps in international air travel and cargo shipping nearly a decade after the Sept. 11, 2001, hijackings in the United States and showed extremists appear to be probing those vulnerabilities.

"The security gap is now for things leaving Yemen," said Riad Kahwaji, head of the Dubai-based Institute for Near East and Gulf Military Analysis. "On the Yemeni side, they'll have a lot to answer for to regain their credibility."

More potential mail bombs

In Washington, D.C., President Barack Obama's top counterterrorism adviser John Brennan, said authorities "have to presume" there might be more potential mail bombs like the ones pulled from planes in England and the U.A.E.

U.S. inspectors were heading to Yemen to monitor cargo security practices and pinpoint holes in the system. An internal report, obtained by The Associated Press, said the team of six inspectors from the U.S. Transportation Security Administration will give Yemeni officials recommendations and training to improve cargo security.

Brennan noted that because of the continuing threat, the world's largest package delivery companies — FedEx and UPS — have suspended air freight from Yemen.

The explosives, addressed to Chicago-area synagogues, were pulled off airplanes in England and the U.A.E. early Friday morning after intelligence officials were tipped off about them, touching off a tense search for other devices.

The package that was stopped in London was nearly caught when it passed through the UPS hub in Cologne, Germany, after police there received a tip-off, German Interior Minister Thomas de Maiziere said Sunday.

By the time German officials received the tip, however, the package was already en route to Britain, and they had to alert their British colleagues.

Germany has now stopped all package deliveries from Yemen.

British Prime Minister David Cameron said he believes the device was intended to detonate on the plane, while Home Secretary Theresa May said the bomb was powerful enough to down the aircraft.

A U.S. official and a British security consultant said Sunday that the device in England nearly slipped past investigators even after they were tipped off, suggesting it was sophisticated enough to escape notice.

Avoided detection

Qatar Airways said the explosives could not have been detected by X-rays or bomb-sniffing dogs and would not have been discovered without the intelligence tip-off.

Al-Qaeda's offshoot in Yemen is suspected of mailing the bombs. The group was behind a failed bombing on a Detroit-bound airliner last Christmas that bore some of the same hallmarks.

The student who was arrested Saturday, Hanan al-Samawi, was released on Sunday after, according to a Yemeni official, the shipping agent said she wasn't the one who signed the shipping documents.

According to a Yemeni security official, at least five other suspects have been arrested and interrogated since Saturday over who might be behind the mail bombs and a number of employees of the shipping companies, including two from FedEx, are being investigated.

Yemen is also asking for more information from Saudi Arabia, which the U.S. said provided the tip-off that thwarted the bombing.