A woman believed to be connected to a plot to send explosive packages bound for the United States has been arrested in the Yemeni capital of Sanaa, according to a Yemeni government official and a reporter with the state news agency.

A female relative of the woman was also being questioned by Yemeni authorities, the government official said. The relationship between the two women was not immediately known.

Believing that a Yemen affiliate of al Qaeda was involved, American and British authorities said explosive devices jammed into ink toner cartridges were powerful enough to bring down a large aircraft. One package was found in Dubai in the United Arab Emirates; the other in England.

But officials weren’t certain whether those behind the plot, who likely would have used cell phones to trigger the devices, wanted to detonate them while the planes were in the air or at their destinations, two synagogues in Chicago, Illinois.

British authorities said they believe East Midlands Airport in central England was simply a conduit for shipment of one device to the United States.

“We believe that the device was designed to go off on the airplane,” Prime Minister David Cameron said. “We cannot be sure about the timing when that was meant to take place. There is no early evidence that that was meant to take place over British soil, but of course we cannot rule it out.”

UK Home Secretary Theresa May said authorities do not believe the perpetrators would have known the location of the device had they detonated it.

Authorities pointed their fingers at al Qaeda in the Arabian Peninsula, which is based in Yemen, a poor Arab nation that has emerged as a major operating base for al Qaeda and other terror groups.

Secretary of Homeland Security Janet Napolitano told CNN Saturday that the plan to send the explosives has the “hallmarks of al Qaeda, the AQAP — they are constantly trying things to test our system.”

Yemen has asked for outside help to thwart terror groups, but the country, the ancestral home of Osama bin Laden, is still used for operations, U.S. officials say. The failed “X-Mas Day Bomber” plot, for example, is believed to be the workings of al Qaeda in the Arabian Peninsula. And in January, the United States and United Kingdom temporarily closed their embassies in Yemen’s capital, Sanaa, because of terror concerns.

U.S. authorities were grateful for a tip from Yemen’s oil-rich neighbor, Saudi Arabia, alerting them to the suspicious packages.

The Saudi government provided U.S. officials with tracking numbers of the two packages, enabling quick tracing to the United Kingdom and Dubai, a source told CNN.

President Barack Obama called King Abdullah on Saturday to thank him, the White House said.

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(Read More: CNN)