A senior US general responsible for bringing down a Chinese spy balloon said on Monday the military had not detected previous spy balloons before the one that appeared on Jan 28 over the United States and called it an "awareness gap."
The Pentagon said over the weekend that Chinese spy balloons had briefly flown over the United States at least three times during President Donald Trump's administration and one previously under President Joe Biden.
Air Force General Glen VanHerck, head of US North American Aerospace Defense Command and Northern Command, said the latest balloon was 200 feet (60 meters) tall and the payload under it weighed a couple thousand pounds.
He did not provide details on previous balloons, including where over the United States they flew.
"I will tell you that we did not detect those threats, and that's a domain awareness gap," VanHerck said.
VanHerck added that US intelligence determined the previous flights after the fact based on "additional means of collection" of intelligence without offering further details on whether that might be cyber espionage, telephone intercepts or human sources.
Senior US officials have offered to brief individuals from the previous administration on the details of previous balloons overflights when Trump was president.
Republican Representative Michael Waltz, who serves on the House of Representatives intelligence committee, said on Sunday that the Pentagon had told him that several Chinese balloon incidents had happened over the past few years, including over Florida.
A US Air Force fighter jet shot down the suspected Chinese spy balloon off the South Carolina coast on Saturday, a week after it first entered US airspace and triggered a dramatic -- and public -- spying saga that worsened Sino-US relations.
VanHerck did not rule out that there could have been explosives on the balloon, but said he did not have any evidence of it either. That risk, however, was a factor in his planning to shoot down the balloon over open water.
Multiple fighter and refueling aircraft were involved in the mission, but only one -- an F-22 fighter jet from Langley Air Force Base in Virginia -- took the shot at 2:39 pm, using a single AIM-9X supersonic, heat-seeking, air-to-air missile.
VanHerck said debris had been collected from an area roughly 1,500 meters (4,920 feet) by 1,500 meters and a number of military vessels were helping gather it.
The US Coast Guard said Monday it was imposing a temporary security zone in the waters off Surfside Beach, South Carolina, in the area where the balloon was shot down.
Officials did not disclose how intact the payload of spying sensors carried by the balloon was after it splashed down in the ocean -- a factor that could determine whether the shoot-down was a success from an intelligence-gathering perspective.