WASHINGTON — Two powerful bombs sent from Yemen appear to have been designed to blow up airliners on their way to the United States and the devices bore the hallmarks of a fugitive Saudi bomb maker who has repeatedly targeted the U.S. and its allies, senior U.S. officials said Sunday,

A team of U.S. and British investigators were expected to arrive in Yemen’s capital Sana early this week to assist Yemeni authorities in investigating the attempted bombings, which were disrupted last week after authorities in Britain and the United Arab Emirates, acting on tips from Saudi and U.S. intelligence, intercepted the packages.

Though initial reports indicated they were shipped aboard cargo jets, Qatar Airways said in a statement Sunday that the package intercepted in the UAE was initially transported aboard a passenger jet that went from Sana, the Yemeni capital, to Doha, the Qatari capital, and then on to Dubai in the United Arab Emirates.

John O. Brennan, the White House’s senior counterterrorism adviser, said the packages were addressed to fictitious people in Chicago “”associated with synagogues.”” But he indicated that investigators were more confident after investigating the devices over the weekend that the bombs were designed to go off before being delivered.

“”We’re looking at the potential that they would have been detonated en route to those synagogues aboard the aircraft as well as at the destinations,”” Brennan said in an interview on CBS’ “”Face the Nation.”” “”But at this point, I think, we would agree with the British that they were designed to be detonated in flight.””

He was referring to statements by senior British officials Saturday that one of the devices, which was intercepted in East Midlands airport in central England, could have been triggered to go off while in the air and that it was powerful enough to bring down an airliner.

On Sunday, authorities in Yemen released 23-year-old Hanan Samawi, an engineering student who had been arrested after her name was discovered on one or both of the packages sent from Sana. A Yemeni official said Sunday she was released because authorities concluded Samawi had not sent the packages.

As investigation of the plot intensified, U.S. officials said their initial findings provided more evidence that al-Qaida in the Arabian Peninsula, an offshoot of the original group created by Osama bin Laden, is probing for weaknesses in U.S. counterterrorism defenses and that it had evolved into one of the most active terrorist organizations from its stronghold in remote and lawless parts of Yemen.

Forensic analysis of the two U.S.-bound bombs hidden inside computer printers indicated they were constructed by Ibrahim Hassan Asiri, a member of al-Qaida in the Arabian Peninsula who is also believed to have built the devices used in two previous attempted attacks, including a failed effort to blow up a U.S. airliner last December, Brennan said.

How the Obama administration will react to the latest threat from Yemen remains unclear. A senior Pentagon official said Sunday that there have been no decisions on changing the current U.S. approach, which relies on U.S. special forces to train Yemeni security forces so they can better deal with the growing militant presence.

The U.S. has also carried out a series of secret strikes with the approval of Yemeni President Ali Abdullah Saleh against al-Qaida leaders in Yemen. Even so, the threat from the country has grown, making it second only to Pakistan as a hiding place for militants, the official said.

“”We have watched al-Qaida move into Yemen for much of the last year, and the threat from AQAP continues to grow,”” said the Pentagon official. Another official said the incident is likely to lead to greater pressure from the U.S. on Saleh to step up covert activities targeting al-Qaida in the Arabian Peninsula.

The U.S. has halted all cargo and mail shipments from Yemen, and security officials in multiple countries were searching shipments Sunday for other bombs, officials said. Asked if there could be any more packages carrying explosives en route, Brennan said all packages coming from Yemen would be checked.

“”We can’t presume that there are none other that are out there, so what we’re trying to do right now is to work very closely with our partners overseas to identify all packages that left Yemen recently,”” Brennan told ABC News’ “”This Week with Christiane Amanpour.””

The intercepted packages were removed from airplanes late Friday in Britain and in the United Arab Emirates after Saudi security officials discovered the plot and tipped off U.S. counterparts.

Both devices contained the high explosive PETN — pentaerythritol tetranitrate, which is an indicator of Asiri’s work.

“”He is a very dangerous individual, clearly somebody who has a fair amount of training and experience,”” Brennan said on ABC’s “”This Week.””

The official Qatar News Agency quoted a statement from the airline saying that the cargo should have been subject to X-ray inspection in Yemen. But the state-owned airline also noted that the explosives discovered were so sophisticated they may not have been detected by standard screening procedures.

Officials in Dubai said in a statement to reporters that the bomb was hidden inside a printer cartridge in a desktop printer and that it contained an electronic circuit and a cell phone chip, but U.S. officials declined to describe the trigger mechanism in either device.

The construction could indicate that Asiri is growing more sophisticated in his bomb designs, two of which have performed poorly before.

Asiri is also believed to have built the bomb hidden in the underwear of a young Nigerian who tried and failed to blow up a US Airways flight from Amsterdam to Detroit last December, and a similar device used in a suicide bombing targeting the Saudi deputy interior minister, Prince Mohammed bin Nayif, in August 2009. The device failed to kill Prince Nayif, though his bodyguard was killed in the blast.

The Christmas Day bomber, Umar Farouk Abdulmutallab, tried to detonate the device in his underwear using a syringe that injected another chemical, though the attack was thwarted by another passenger.

The latest devices appear to have relied on electronic triggering mechanisms, rather than on chemical reactions. The bombs “”didn’t require any additional components or didn’t require anybody to go in and sort of manually press a syringe or something else,”” Brennan said on “”Fox News Sunday.””