(CNN) -- The infiltration of a Middle Eastern terror network by a mole who helped foil a plot to blow up a U.S.-bound plane was a "phenomenal," "brilliant" and "powerful" success, experts said Wednesday.
It's unclear how much of the credit should go to the United States or to Saudi Arabia, for whom sources say the mole was working, but both countries have delivered a practical and psychological setback to al Qaeda in the Arabian Peninsula, analysts on the region said.
Western officials describe that affiliate as al Qaeda's most dangerous.
"It's a devastating blow to al Qaeda, though not a fatal one," said Juan Zarate, who was deputy national security adviser for combating terrorism under President George W. Bush.
"What this demonstrates is that we have the ability to get on the inside."
And the plot, by the same group that launched a failed attempt to bomb a U.S.-bound airliner on Christmas 2009, demonstrates the continued "rise of the affiliates," he said. "We have a decimated al Qaeda core -- the al Qaeda of 2001 that we have battled and really dismantled in many ways has metastasized and is now presenting itself in this regional form."
This latest intelligence success marks the deepest known penetration into al Qaeda, said Ali Soufan, a former FBI official who oversaw highly sensitive international terrorism cases. But he noted many intelligence efforts remain secret.
"It's a major success for the CIA and for the intelligence community," he said. And, he noted, as in this case with Saudi Arabia, "overseas most of our work is done in cooperation with friendly services."
Of the al Qaeda affiliate groups trying to carry out terrorist operations today, al Qaeda in the Arabian Peninsula is the closest version to the network Osama bin Laden led, Soufan said.
Bruce Riedel, who spent 30 years in the CIA and was a senior adviser on the Middle East to four presidents, said thwarting the bomb plot is "primarily a Saudi success story" -- and not their first.
"They foiled the AQAP plot in October 2010 to send bombs to the U.S. on FedEx and UPS planes," he noted.
That plot was foiled by an informant. Some details remain unknown.
This time, Riedel said, Saudi intelligence managed to "get access to AQAP's plot and actually get the bomb."
Still, thwarting this attack doesn't damage the organization substantially in the big picture, analysts said.
"While this is a good technical success, the harsh reality is that in Yemen, al Qaeda in the Arabian Peninsula is growing, getting more powerful, recruiting more assets and taking advantage of the fact that Yemen is essentially the Humpty Dumpty of the Arabian Peninsula -- it's falling apart, broken," said Riedel, now a senior fellow at the Brookings Institution.
CNN terrorism analyst Paul Cruickshank added that while it is a "big intelligence success" for the United States and Saudi Arabia, "there's a limit to their success as well."
The operation did not lead intelligence services to Ibrahim al-Asiri, the chief bomb maker for al Qaeda in the Arabian Peninsula, or to the location where he makes the bombs.
"They were able to take out Fahd al-Quso, who's a senior operational planner in the group, but they were not able to take out this very dangerous bomb maker who's ingenious at making bombs," Cruickshank noted.
Information from the mole led to a CIA drone strike Sunday in Yemen that killed al-Quso, 37, a senior operative of the al Qaeda affiliate. He was a suspect in the 2000 bombing of the USS Cole in Yemen. He was convicted in a Yemeni court but escaped from jail.
All the analysts who spoke to CNN expressed concern that a mole's involvement was leaked to the media.
"I think authorities, particularly the CIA, would rather not talk about this right now," said Zarate, now a senior adviser on counterterrorism for the Center for Strategic and International Studies.
These kinds of sources "can lead to additional counterterrorism successes or insights," he said. "So the fact that this is now front page news certainly doesn't help."
Soufan, who runs a consultancy group on security issues, said, "When you're doing operations like this, you have to do whatever you can do to protect sources and methods -- not only of the CIA but also of the other intelligence services that were involved in this. Because down the road they will be hesitant to cooperate with us."
However, Zarate said, there may be a bit of a silver lining in the leak. "I think what this will do is it will increase the amount of vigilance and mistrust within al Qaeda circles to outsiders. They need outsiders to supplement their ranks and allow them to plot against the West. ... It will create layers of distrust and will create inefficiencies," Zarate said.