The Chinese balloon shot down off the South Carolina coast was part of a large surveillance programme that China has been conducting for “several years”, the Pentagon said.
When similar balloons passed over US territory on four occasions during the Trump and Biden administrations, the US did not immediately identify them as Chinese surveillance balloons, said Brigadier General Pat Ryder, the Pentagon press secretary.
But he said “subsequent intelligence analysis” allowed the US to confirm they were part of a Chinese spying effort and learn “a lot more” about the programme.
He refused to provide any new details about those previous balloons. When pressed, he would only say that the balloons flew over “sites that would be of interest to the Chinese”.
One of the possible incidents was last February.
Major General Kenneth Hara, the adjutant general in Hawaii, tweeted about a balloon over Kauai a year ago.
He said US Indo-Pacific Command “detected a high-altitude object floating in air in the vicinity of the Hawaiian Islands” and sent up aircraft to intercept it. He said they visually confirmed it was an unmanned balloon with no identification markings.
Brig Gen Ryder declined to say whether this was one of the four previous incidents that the US had discussed. Pacific Air Forces, the Air Force command in the Indo-Pacific, said that balloon was not shot down.
The recent balloon was shot down by a US military fighter jet on Saturday. The navy and coastguard are still working to recover pieces of the downed balloon so they can be analysed.
Brig Gen Ryder said North American Aerospace Defence Command began tracking the recent balloon as it approached US airspace.
It passed north of the Aleutian Islands on January 28 and moved largely over land across Alaska and then into Canadian airspace before crossing back into the US over northern Idaho on January 31, US officials have said.
Top administration officials were briefing members of Congress on the Chinese balloon surveillance programme in classified sessions on Wednesday and Thursday.
Secretary of state Antony Blinken said the US has briefed dozens of countries on the programme, which officials said has been active over five continents.
“The United States was not the only target,” he said at a news conference with visiting Nato chief Jens Stoltenberg.
Mr Blinken said he and Mr Stoltenberg had spoken about the “systemic and tactical challenges” that China poses to the alliance and the importance of combating them.
China claims it was a civilian balloon used for meteorological research and sharply criticised the US for shooting it down.