Afghan government forces could lose the single most important military advantage they have over the Taliban — air power — when private contractors and U.S. troops leave the country in coming weeks, NBC News reported Sunday.

Roughly 18,000 foreign contractors in Afghanistan provide an array of key services to the Afghan security forces, but they are expected to leave the country along with U.S. and NATO troops in the coming weeks.

NBC reported that without the help of foreign contractors, Afghan forces will no longer be able to keep dozens of fighter planes, cargo aircraft, U.S.-made helicopters and drones flying for more than a few more months, according to military experts and a recent Defense Department inspector general’s report.

While the Biden administration has vowed to keep up U.S. financial support for the Afghan army and police, and Afghan officials say they are able to defend the country against the Taliban, the departure of contractors represents a potentially devastating blow for the Afghan government in its fight against the Taliban, NBC reported.

According to Bradley Bowman, senior director of the center on military and political power at the Foundation for Defense of Democracies think tank, air power is the Afghan government’s main competitive edge in its fight against the Taliban.

Bowman, a former U.S. Army officer and Black Hawk helicopter pilot who served in Afghanistan said with the withdrawal of contractors “we’re talking about the more or less grounding of the Afghan Air Force.”

“If we don’t help them maintain those aircraft, then the Afghan security forces will be deprived of that advantage and that could have a decisive impact on the battlefield and ultimately on the state of the Afghan government,” he told NBC.

Under the U.S.-Taliban deal signed last year during the Trump administration, the U.S. pledged to withdraw all American and allied troops as well as all non-diplomatic staff including “trainers, advisers, and supporting services personnel.”

While Pentagon officials have said that the Biden administration is looking at options for supporting the Afghan security forces from afar, neither U.S. nor Afghan officials have announced any definite arrangements.

Afghan officials have also not yet announced any new arrangements with outside firms to maintain U.S.-supplied aircraft and military equipment.

NBC reported that Afghanistan’s embassy in Washington did not respond to requests for comment.

Defense Secretary Lloyd Austin and senior officials have long acknowledged the “critical role” played by the Afghan Air Force and other military aircraft, Pentagon press secretary John Kirby told NBC News, adding that the Defense Department will continue to provide the resources they need.

The administration’s budget request submitted to Congress last week, he said, “fully funds contracted logistics support for the Afghan aviation fleet so the Afghan government can maintain its advantage in the air.”

But Jonathan Schroden from the Center for Naval Analyses, a federally funded research center, told NBC: “In the absence of contract maintenance support, within some number of months, you will have an Afghan Air Force that has pretty significantly reduced capability, i.e. you can’t fly, and an Afghan army that can’t move.”