Al Qaeda could rebuild in Afghanistan in a year or two, U.S. officials say.

Al Qaeda could rebuild inside Afghanistan within one to two years, top intelligence officials said Tuesday, noting that some members of the terror group have already returned to the country.

Earlier in the year, top Pentagon officials said Al Qaeda could reconstitute within two years, then told lawmakers after the fall of the Afghanistan government they were revising that timeline.

The new timeline is not a radical shift, but reflects the reality that the Taliban has a limited ability to control the borders of Afghanistan. While the Taliban have long fought the Islamic State affiliate, they are established allies of Al Qaeda. Though the Taliban pledged in the February 2020 peace agreement with the United States not to let Afghanistan be used by terror groups, analysts have said such promises ring hollow.

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

David S. Cohen, the deputy director of the C.I.A., said the difficult part of the timeline question was to know when Al Qaeda or the Islamic State affiliate in Afghanistan would “have the capability to go to strike the homeland” before they could be detected.

The C.I.A. is keeping a keen watch of “some potential movement of Al Qaeda to Afghanistan,” Mr. Cohen said.

Mr. Cohen did not identify specific Qaeda members who have traveled back to Afghanistan since the fall of the American-backed government. But Osama bin Laden’s former security chief, Amin al Haq, who served with bin Laden during the battle of Tora Bora, was seen on video returning to the Afghan province of Nangarhar last month.

On Monday, speaking at the same conference, Avril D. Haines, the director of national intelligence, said that Afghanistan was not the greatest terror threat facing the United States. Yemen, Somalia, Syria and Iraq, she said, all posed more substantial threats.

The C.I.A. will have to increase its reliance on collecting intelligence from afar, in so-called “over the horizon” operations, Mr. Cohen said. He added the agency hoped to do its work — including rebuilding informant networks — closer to Afghanistan. “We will also look for ways to work from within the horizon, to the extent that is possible,” he said.

Ramping up that intelligence collection in Afghanistan will have to occur, General Berrier said, at the same time as agencies improve their ability to monitor China and Russia.

“We’re thinking about ways to gain access back into Afghanistan with all kinds of sources,” the general said. But he added, “We have to be careful to balance these very scarce resources with this pivot to China, and to Russia.”