The U.S. intelligence community believes that the recently recovered Chinese spy balloon is part of an extensive surveillance program run by the Chinese military, the Department of Defense said Wednesday.

Pentagon Press Secretary Brig. Gen. Pat Ryder criticized China on Wednesday for its efforts to gather data about American military bases through its latest surveillance program, which includes a number of similar balloons, and is in part run out of the small Chinese province of Hainan.

"This just demonstrates why [China] continues to remain our pacing challenge. And I think that they have a lot of explaining to do when it comes to conducting these types of programs and violating nations' airspace and sovereignty," Ryder told reporters.

The U.S. does not know the precise size of the fleet of Chinese surveillance balloons, but CNN reports that the program has conducted at least two dozen missions over at least five continents in recent years.

The usage of spy balloons can be attributed to some advantages they hold over the satellites that orbit the earth in regular patterns, according to the New York Times.

Balloons fly closer to the ground and drift with wind patterns, which are not as predictable to militaries and intelligence agencies as the fixed orbits of satellites, and they can evade radar. They can also hover over areas while satellites are generally in constant motion. Simple cameras on balloons can produce clearer images than those on orbital satellites, and other surveillance equipment can pick up signals that do not reach the altitude of satellites.

In recent years, at least four balloons have been spotted over Hawaii, Florida, Texas, and Guam — in addition to the one tracked last week. Three of the four instances took place during the Trump administration but were only recently identified as Chinese surveillance airships.

The spy balloon shot down Saturday first entered U.S. airspace over Alaska on Jan. 28. It crossed north of the Aleutian Islands, back over mainland Alaska, over Canada, and then over northern Idaho last week, but the government did not acknowledge its presence until NBC News reported last Thursday that the Pentagon was tracking the balloon over Montana.

China has officially said the balloon was being used for meteorological and research purposes, rather than spying, and that wind pushed it off course. Navy divers recovered the balloon debris off the South Carolina coast on Saturday.