The US military is closely watching the security situation in Afghanistan after fresh gains by the Taliban against government forces as the Pentagon withdraws, top officials said Wednesday

Speaking in Congress, Joint Chiefs Chairman General Mark Milley said 81 of 419 district centers had come under the control of the insurgents.

While the Taliban say they have added dozens of districts in the past two months alone, Milley said 60 of those had been captured last year before the United States began its final pullout.

He noted that the Islamist fighters had not captured a single provincial capital.

In the same hearing Defense Secretary Lloyd Austin made clear that the Taliban's gains were not interfering with the final withdrawal of US troops after nearly two decades.

The pullout is already more than half-done and is to be completed by September.

"We are focused, and the task that we have at hand is to conduct our retrograde in a safe, orderly and responsible fashion," Austin told the panel.

"We've developed a very detailed plan to do that. And we have accomplished the task according to plan thus far, and really provided for the safety of not only our forces but our allies as well," he said.