Since Afghanistan was taken over by the Taliban top intelligence officials are speculating that Al Qaeda, the terrorist group behind the 9/11 attacks, could likely rebuild within one to two years enough capabilities to threaten the United States.

Fox News reports:

“The current assessment probably conservatively is one to two years for al Qaeda to build some capability to at least threaten the homeland,” said Director of the Defense Intelligence Agency Lt. Gen. Scott D. Berrier during Tuesday’s National Security Summit.

Officials say that members of the terrorist group have already started to return to the country amid the Taliban takeover, speeding the timeline for which the group could begin to pose a renewed threat.

While both al Qaeda and ISIS-K have a presence in Afghanistan, only al Qaeda has an established alliance with the Taliban. It is still unclear how much effort the Taliban will put into keeping the terrorist group in check, though they pledged during the peace agreement with the U.S. to not allow the country to become a haven for terrorist groups, a pledge some officials do not trust the Taliban to keep now that U.S. forces have departed Afghanistan.

Deputy director of the CIA David S. Cohen said the agency is watching “some potential movement of al Qaeda to Afghanistan” but noted it is hard for the CIA to assess a timeline for when they or ISIS-K would “have the capability to go to strike the homeland” before the agency could detect the threat.

Cohen said that since the U.S. no longer has a presence on the ground, intelligence officials will be working to develop new ways to work “from the horizon.” The United States will be developing over-the-horizon intelligence abilities to monitor activity in Afghanistan as well as other potential threats such as China and Russia.