The secretary of the Air Force said Friday that her service is under "tremendous strain" and she is worried about whether it is ready to fight adversaries with developed air defenses.

The Air Force has been focused on waging air campaigns in Iraq, Syria, and Afghanistan, where U.S. air power easily dominates. It's also been managing U.S. nuclear weapons, Secretary Heather Wilson told reporters at the Pentagon.

"So what happens if there is a circumstance that is heavily contested? I worry about that. I think we should all worry about that," she said.

The secretary said the lack of readiness for a high-end conflict with advanced adversaries such as China, Iran, and Russia could lead to higher Air Force casualties.

"That doesn't mean we won't go, it means fewer will come back. I think we need to understand that," Wilson said.

The Air Force and other branches of the military have repeatedly warned Congress that years of defense budget caps and stop-gap budget measures have left them dangerously overburdened and underfunded.

President Trump has requested a budget increase focused on shoring up the depleted forces and Congress is weighing even larger spending hikes, though the future of the funding remains uncertain due to deep political divisions on Capitol Hill.