North America Aerospace Defense Command (NORAD), a combined U.S.-Canada airspace warning and defense organization, did not recognize previous instances of Chinese surveillance balloons entering U.S. territory, NORAD and U.S. Northern Command chief Gen. Glen VanHerck confirmed Monday.

Previous Chinese spy balloon incursions went unnoticed until after the craft had exited U.S. airspace, Biden administration officials, speaking anonymously, said Sunday, according to The Wall Street Journal. The intelligence community had retroactively identified the existence of three suspected Chinese spy balloons entering U.S. territory under former President Donald Trump and once at the beginning of the Biden administration, VanHerck confirmed in a briefing Monday.

“Every day as a NORAD commander, it’s my responsibility to detect threats to North America,” VanHerck said. “We did not detect those threats, and that’s a domain awareness gap that we have to figure out.”

The intelligence community “after the fact” assessed balloon threats through “additional means of collection,” he said. Intelligence agencies alerted NORAD of balloons that had previously approached or transited North America, according to VanHerck, but the general did not say when those assessments were completed.

However, some Trump administration national security officials have publicly denied knowledge of previous alleged Chinese surveillance balloons intruding on U.S. territory. (RELATED: Trump Officials Offer Inconsistent Explanations About Prior Chinese Spy Balloons)

All three national security advisers under Trump — John Bolton, H.R. McMaster and Robert O’Brien — said they had no knowledge of balloon incursions, according to the WSJ.

“I had no knowledge of any incursions into U.S. airspace as national security adviser, either during my time as national security adviser or before I got there, nor was I briefed on any China issues like this,” O’Brien said.

“It never happened,” former acting Director of National Intelligence (DNI) Richard Grenell told Newsmax, adding that he has declined the Biden administration’s offer of a post-facto briefing on the apparent earlier incursions.

“As to the alleged three instances of China flying surveillance balloons over the U.S. during the Trump administration, I noted that Mr. Trump has denied the claim,” Chinese Foreign Ministry spokesperson Mao Ning said Monday.

NORAD did detect the most recent balloon as it approached Alaska and first penetrated U.S. airspace, VanHerck said.

“It was my assessment that this balloon did not present a physical military threat to North America,” the general said in answer to a question on why the U.S. did not down the balloon over Alaska. “Therefore I could not take immediate action because it was not demonstrating hostile acts or hostile intent.”

NORAD was granted special authorities to collect intelligence on the balloon as it traversed U.S. territory, he added. The Air Force finally shot down the balloon on Saturday off the coast of South Carolina into shallow waters, allowing the military to retrieve sections of the craft’s surveillance equipment.

The U.S. military has established a 1,500 meter by 1,500 meter estimated collection plane where they are gathering debris from the craft, VanHerck said. The balloon portion was estimated at 200 feet in height and carried a surveillance payload roughly the size of a jetliner, weighing several thousand pounds.

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