Yemen has arrested two women suspected of mailing the explosive parcels from the country to the US that sparked a global security alert, sources say.
A woman was detained with her mother, her defence lawyer said, adding that she was a "quiet student" with no known links of religious or political groups.
The arrests took place on Saturday in the Yemeni capital Sanaa, after security forces surrounded a house where the suspect believed to have sent the packages was hiding.
A Yemeni security official said the woman had been traced through a telephone number she left with a cargo company.
Ali Abdullah Saleh, the Yemeni president, confirmed her arrest, saying: "Yemen is determined to fight terror but will not allow anyone to intervene in its affairs."
Security officials have been on high alert since the UK and the United Arab Emirates intercepted two packages containing explosive material that were being shipped by air from Yemen to synagogues in Chicago.
The packages were discovered on Friday at East Midlands Airport, in Nottingham, north of London, and at a courier facility in Dubai.
Earlier on Saturday, Yemeni authorities seized and examined up to 26 suspect parcels. They are also engaged in a heated search for al-Qaeda fighters in Yemen, where Anwar al-Awlaki, a US-born Muslim religious leader, is named as being linked to the plot.
The failed plot has prompted scrutiny of airport security in the UK, where Theresa May, the home secretary, announced a ban on all unaccompanied cargo coming from Yemen into the country.
Security has also increased in the US, where the postal service has temporarily stopped accepting inbound mail originating in Yemen.
Al Jazeera's Monica Villamizar, reporting from Washington, DC, said that US authorities now consider Yemen and al-Qaeda in the Arabian Peninsula (AQAP) to be "more of a threat to the US and its interests now than even Afghanistan and Pakistan".
She also said that US investigators will now look at previously shipped packages from Yemen to determine if they were used as a "dry run" by al-Qaeda.
Police in Dubai said the package they found bore the hallmarks of al-Qaeda. They also said that the ink cartridge found at the sorting facility was packed with pentaerythritol tetranitrate, or PETN, confirming what Jane Harman, a Democratic congresswoman from California who was briefed on the incident, had told the New York Times newspaper earlier.
PETN is the same substance that was packed into the underwear of Umar Farouk Abdulmutallab, the Nigerian man who attempted to ignite a bomb on board an airliner over the US on December 25 last year. The police said the explosive materials were wired to a mobile phone SIM card hidden inside the printer.
The package found in the UK was on board a UPS cargo aircraft, while the other, in Dubai, was found in a FedEx sorting facility.
Al Jazeera's Dan Nolan, reporting from Dubai, said that authorities were concerned given the volume of air traffic that passes through the emirate.
Bob Ayers, an independent security analyst, told Al Jazeera that cargo is subject to less stringent security screening than passenger luggage.
The screening of cargo has been a point of debate in the US; in 2007, congress directed the Transportation Security Administration to screen all cargo carried on passenger flights beginning this year, according to US media.
"Cargo is in big pallets, it's wrapped, its prepared for shipment," Ayers said. "You can't X-ray the large pallet in many cases. You don't tear it apart because its already been pre-packaged, so cargo has always been less rigorously inspected than baggage going into a passenger aircraft."
Both UPS and FedEx said they had halted all packages being sent from Yemen to the US while the incident is investigated.
In September, a large fire broke out in the cargo hold of a UPS cargo jet shortly after it took off from the Dubai airport. The plane crashed, killing both crew members. Our correspondent said that investigators will probably now check to see if any cargo from Yemen was on board.
Source: Al Jazeera and Agencies