The United States government has begun a land evacuation of American civilians who are in Sudan amid a growing civil conflict.

A U.S. official told Fox News that there's an ongoing effort to bus a large group of Americans to the Red Sea, where Port Sudan is located.

It's unclear how many Americans are being evacuated or how many buses are being used in the effort.

Pentagon press secretary Brig. Gen. Pat Ryder said during a Thursday press briefing that U.S. Africa Command was flying unmanned ISR drones over potential land routes in Sudan, adding that U.S. Naval assets are off Sudan's coast in the case of an evacuation.

"We have focused our efforts on support to overland routes," Ryder said. 

This is a developing story.