The airline spokesman disclosed the information on condition of anonymity in line with the company's standing policies on conversations with the media. He did not give any timeframe for the two flights in question. The airline operates daily passenger flights from Yemen that could also carry courier packages.

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

 I think we have to presume that there might be and therefore we have to take these measures 

US counterterrorism adviser John Brennan

In Washington, President Barack Obama's counterterrorism adviser John Brennan said Sunday that authorities "have to presume" there might be more potential mail bombs like the ones pulled from planes in England and the United Arab Emirates.

"I think we have to presume that there might be and therefore we have to take these measures. But right now we do not have indications that there are others that are out there," Brennan told NBC's "Meet the Press" news show.

"We are trying to get a better handle on what else might be out there. That's why we've taken exceptionally prudent measures in my mind as far as preventing packages coming in to the United States from Yemen," he said.

Yemeni police arrested a woman on suspicion of mailing the pair of bombs powerful enough to take down airplanes.

Investigators were hunting Yemen for more suspects tied to al-Qaeda and several U.S. officials identified the terrorist group's top explosives expert in Yemen as the most likely bomb maker.

It still wasn't clear whether the bombs, which officials said were wired to cell phones, timers and power supplies, could have been detonated remotely while the planes were in the air, or when the packages were halfway around the world in the U.S. But the fact that they made it onto airplanes showed that nearly a decade since the Sept. 11, 2001 attacks, terrorists continue to probe and find security vulnerabilities.

The packages were addressed to two synagogues in the Chicago area. But British Prime Minister David Cameron said Saturday that he believes the explosive device found at the East Midlands Airport in central England was intended to detonate aboard the plane.

British Home Secretary Theresa May added that the bomb was powerful enough to take down the plane. A U.S. official said authorities believe a second device found in Dubai was similarly potent.

Yemeni President Ali Abdullah Saleh told reporters that the United States and United Arab Emirates had provided intelligence that helped identify the woman suspected of mailing the packages.

A Yemeni security official said the young woman was a medical student and that her mother also was detained.

The police action was part of a widening manhunt for suspects believed to have used forged documents and ID cards, Yemeni officials said. One member of Yemen's anti-terrorism unit said the other suspects had been tied to al-Qaeda.