WASHINGTON — The American military’s extensive use of drones against the Islamic State and other terrorist groups has resulted in a shortage of Air Force pilots and other personnel to operate the aircraft, leading the Pentagon to rely more on private contractors for reconnaissance missions in Afghanistan and Iraq.

Since the Sept. 11, 2001, attacks, the Pentagon has used contractors to perform many duties traditionally carried out by uniformed personnel, like protecting military bases and feeding service members. The contractors who are now serving as drone pilots are based in the regions where the drones are flown, and they are legally prohibited from being “trigger pullers” and firing weapons, Air Force officials said. But there is no limit on the type of reconnaissance they can perform, and they are providing live video feeds of battles and special operations.

As the Obama administration has accelerated its campaign against the Islamic State in Iraq, Syria and Libya over the past 10 months, the Pentagon has added four drones flown by contractors to the roughly 60 that are typically flown every day by uniformed Air Force personnel.

Over the next two years, the Pentagon plans to add six more operated by contractors, the officials said. The number and identities of contractors working on the drone flights are considered classified information, the Air Force said. But Pentagon officials said there are at least several hundred contractors, many of them former drone or fighter pilots who are making double or triple their military salaries.