"My military estimate is ... that the conditions are likely to develop of a civil war," Chairman of the Joint Chiefs of Staff Gen. Mark Milley told Fox News in an interview in Ramstein, Germany aired on Saturday. He also cast doubt on Taliban's future governance.
"I don't know if the Taliban is going to (be) able to consolidate power and establish governance," said the US general.
"I think there's at least a very good probability of a broader civil war and that will then, in turn, lead to conditions that could, in fact, lead to a reconstitution of al-Qaeda or a growth of ISIS or other myriad of terrorist groups," he added.
He said a resurgence of terrorism might come out of the region "within 12, 24, 36 months."
On Aug. 31, the US announced the completion of its efforts to withdraw all of its forces from Afghanistan, bringing to an end the longest war in American history.
Two weeks before the pullout, the Taliban took over the capital Kabul, sending panic among the public as thousands flocked to the city's airport in a move to escape the country.
Some 130,000 people, including Americans and Afghans, have been flown out of the country as part of a massive evacuation operation.
Source: Anadolu Agency