With the Taliban steamrolling across Afghanistan, U.S. defense officials are concerned that a Taliban takeover of the country will allow Al Qaeda to rebuild and consolidate, creating security concerns well outside Afghan borders.
Nearly 20 years after it planned the Sept. 11 attacks from Afghanistan, Al Qaeda has a diminished presence in the country, which senior U.S. officials estimate at only 200 to 300 members.
"They're really not a very large or what we would consider a capable contingent," one of the officials said.
But the security vacuum left by the withdrawal of U.S. military forces could create an opening for Al Qaeda and other terrorist groups to reorganize, the officials say.
If the Taliban take over the government, intelligence about Al Qaeda is likely to become even scarcer. And while the U.S. will still maintain authority to strike Al Qaeda targets in Afghanistan, the lack of a robust U.S. presence on the ground will hamper the ability to identify potential targets, a senior defense official said.
In an interview last month after he took over as head of U.S. forces in Afghanistan, Marine Gen. Frank McKenzie said Al Qaeda is still a principal focus of the U.S. military in the region.
"What we're here for is to prevent Al Qaeda and ISIS from being able to reconstitute in the ungoverned spaces, generally of eastern Afghanistan, and be able to plot attacks against our homeland," McKenzie said in the capital, Kabul. "That threat is still here today."
McKenzie said U.S. counterterrorism forces had made it impossible for Al Qaeda to regenerate and carry out its plans against the West.
"If that pressure comes off, I believe they're going to regenerate," he said. "And I think it's only a matter of time before we see them assert themselves and begin to plan attacks against our homeland."
With Al Qaeda in a rebuilding phase in Afghanistan, it is difficult for it to reorganize quickly, the senior U.S. officials said. And while the Al Qaeda ideology emphasizes attacks against the Western world, that is not the current strategy for its fighters in Afghanistan, the senior U.S. officials said.
"They're emphasizing this idea that let's get our local houses in order in order to consolidate our positions," a senior U.S. official said. "And then we will think about global jihad, because that's still on their minds."
The officials stressed that Al Qaeda in Afghanistan is unlikely to have the capability to carry out an attack on foreign soil against the U.S. or another Western country any time soon.
"Within the next 12 months, we think, the threat is low for them to try to attempt from Afghanistan some kind of transnational attacks against the West," one of the officials said.
But the officials believe that a Taliban government in Afghanistan would not stop Al Qaeda from rebuilding and that it will eventually work toward attacks on foreign soil again.
The terrorist group has been severely hobbled by two decades of airstrikes and counterterrorism pressure. Al Qaeda's senior leaders and operational planners and many fighters have been killed or have fled the country.
Osama bin Laden, the founder of the group, who masterminded the 9/11 attacks, was killed in 2011. Al Qaeda's current leader, Ayman al-Zawahri, is believed to be alive but unwell, according to a U.N. Security Council report released late last month.
The report went on to say that Al Qaeda is believed to be in at least 15 Afghan provinces, primarily in the east and the south.
"Although there has been only limited relocation of foreign terrorist fighters from [Syria and Iraq] to other conflict zones, member states are concerned about the possibility of such movement, in particular to Afghanistan, should the environment there become more hospitable to ISIL or groups aligned with Al Qaeda," the report says. ISIL, like ISIS, is one of several renderings of the name of the Islamic State terrorist group.
McKenzie said last month that he does not believe the Taliban will stop Al Qaeda from using Afghanistan to strengthen and rebuild.
"I've seen nothing that makes me believe they're actually going to do that," McKenzie said. "I know they talk about doing it. I'd like to believe that they will, but I've always wanted the Taliban not to be governed by what they say but rather what they do, and they have not done that to date."