Reports were circulating of a senior British source who has raised concerns about an Islamic State affiliate in Afghanistan called Islamic State Khorasan, or ISIS-K.
Ministers have voiced their fears about a security threat surrounding the evacuation efforts.
While US and UK forces control the airfield, they have been relying on the Taliban to help secure access to the terminal.
President Joe Biden has said the United States remains on pace to finish evacuations from Afghanistan by August 31 but left open the chance of extending the deadline.
In remarks at the White House, Mr Biden said the US was racing to meet the deadline as concerns mount over the threat of militant attacks.
“The sooner we can finish, the better,” he said. “Each day of operations brings added risk to our troops.”
Continued coordination with the Taliban remains crucial to meeting the deadline, he said, but he called it a “tenuous situation” with a “serious risk of breaking down as time goes on”.
Taliban spokesman Zabihullah Mujahid added pressure with the warning no evacuations will be allowed following the deadline.
During a press conference in Kabul, he said: “August 31 is the time given and after that it’s something that is against the agreement.
“All people should be removed prior to that date. After that we do not allow them, it will not be allowed in our country, we will take a different stance.”