At least three suspected Chinese spy balloons flew over the US undetected during the Donald Trump presidency, defence officials have said.
The US did not detect the balloons at the time, said Gen Glen VanHerck, citing a “domain awareness gap”.
They may have initially been classified as UFOs, according to the New York Times and Bloomberg.
The US has since classified them as surveillance balloons, based on additional intelligence.
Gen VanHerck, the Pentagon official responsible for US airspace defence, said on Monday there was a gap in military intelligence at the time.
“It’s my responsibility to detect threats to North America. I will tell you that we did not detect those threats,” he said.
A suspected Chinese spy balloon was shot down by the US military over the weekend after it spent days travelling through American airspace.
The US Navy is still working to recover the debris off the coast of South Carolina.
The balloon incident has strained US-China relations, with Secretary of State Antony Blinken last week cancelling a planned trip to Beijing.
It would have been the first high-level meeting of American and Chinese officials there in years.
The White House has credited a directive by President Joe Biden to intelligence agencies to increase efforts to identify spying operations in the US with helping to flag the recent incident..
“We enhanced our capacity to be able to detect things that the Trump administration was unable to detect,” said White House national security advisor Jake Sullivan.
On Monday, John K Kirby, a US National Security Council spokesman, confirmed suspected surveillance balloons flew over the US during Mr Trump’s time in office.
“From every indication that we have, that was for brief periods of time — nothing at all like what we saw last week in terms of duration,” he said.
On Truth Social, Mr Trump dismissed the reports as “fake disinformation”.
Mark Esper, who served as defence secretary under Mr Trump, told CNN on Friday that he was “surprised” to hear of reports of spy balloon from that time.
“I don’t ever recall somebody coming into my office or reading anything that the Chinese had a surveillance balloon above the United States,” he said.
Chinese officials have denied that the balloon that crossed the continental US last week was used for spying purposes, claiming it was a weather balloon that had flown off course.