President Barack Obama's counterterrorism adviser 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.
The foiled plot "certainly bears the hallmark" of al-Qaida's Yemen branch, known as al-Qaida in the Arabian Peninsula, and the terrorist group is "still at war with us and we are very much at war with them," deputy national security adviser John Brennan said.
"We're trying to get a better handle on what else may be out there," Brennan told NBC's "Meet the Press" as he made the rounds of the Sunday talk shows representing the Obama administration in the wake of the latest terrorist scare. "We're trying to understand better what we may be facing."
U.S. intelligence officials believe the suspected bombmaker is a Saudi named Ibrahim Hassan al-Asiri.
Forensic analysis indicates that the same bombmaker also constructed the devices used in the failed bombing on a Detroit-bound airliner last Christmas and the attack on Saudi Arabia's counterterrorism chief last year, Brennan said. All three bombs contained the explosive PETN.
The person assembling these devices, he told ABC's "This Week," is "clearly somebody who has a fair amount of training and experience and we need to find him and we need to bring him to justice."
Brennan added that the devices were able to go off "at a time of the terrorists' choosing _ including when a plane was in flight or when the packages reached their final destination. "They could have brought those planes down," he said. "It is my understanding that these devices did not need someone to actually physically detonate them."
Brennan noted that because of the continuing threat, the world's largest package delivery companies _ FedEx and UPS _ have suspended air freight from Yemen.
"I think prudence tells us to make sure that we're doing everything possible to screen cargo that might be coming from that part of the world even more rigorously than we have. And we currently have put a hold on any cargo that is coming to the United States that originated in Yemen," Brennan told CBS' "Face the Nation."
Police in Yemen have arrested a young woman on suspicion of mailing the bombs. They also detained her mother.
While he said "we feel good" about the steps taken since the thwarted plot, "I think we have to presume there might be" additional bombs.
"They are a dangerous group. They are a determined group. They are still at war with us and we are very much at war with them. They are going to try to identify vulnerabilities that might exist in the system," he said.
He told CNN's "State of the Union" that "it would be very imprudent ... to presume that there are no others (packages) out there."
Speaking about the Yemen branch, he said the U.S. "will destroy that organization as we are going to destroy the rest of al-Qaida."
Brennan said authorities were trying to determine whether the planes were the intended targets. The packages with the explosives were addressed to Chicago-area synagogues.
He said the two bombs, powerful enough to bring down a plane were "very sophisticated" in the way they were designed and concealed.
"They were self-contained. They were able to be detonated at a time of the terrorists' choosing," Brennan said.
He also said that in light of the bombs found Friday, the National Transportation Safety Board and terrorism investigators were re-examining the UPS cargo jet that crashed in Dubai in September.
Investigators in the United Arab Emirates said Sunday there was no evidence that an explosion caused that crash.
The U.S. officials are also headed to Yemen to monitor cargo security practices and pinpoint holes in the system.
A team of six inspectors from the Transportation Security Administration will give Yemeni officials recommendations and training to improve cargo security, according to internal government report obtained by The Associated Press.
The report also says the agency is considering extending its security directive to increase inspection of cargo for all flights through Nov. 8.