President Joe Biden ordered a high-altitude object to be shot down after it was tracked over Alaska on Friday.
“The Department of Defence was tracking a high-altitude object over Alaska airspace in the last 24 hours,” White House National Security Council spokesman John Kirby told reporters.
The object was flying at an altitude of 12,000 metres and was roughly the size of a small car, Mr Kirby said.
The origins of the aircraft were unknown.
“I have no idea,” Mr Kirby said of who may have operated the aircraft.
“We do not know who owns it, whether state owned or corporate owned. We don't understand the full purpose.”
Mr Kirby did not say whether or not the object was a balloon.
The US military on Thursday night sent a plane to observe the object and determined it was not manned.
Mr Kirby said the object then fell on to frozen US territorial waters, meaning retrieval of debris should be possible.
“Fighter aircraft assigned to US Northern Command took down the object within the last hour,” he said, meaning it was destroyed around 2pm ET.
The incident comes after the military shot down a suspected Chinese spy balloon at the weekend. Mr Kirby said the US had not contacted China about the object shot down over Alaska.
The US on Friday blacklisted five Chinese companies and a research institute in retaliation for the suspected spy balloon.
They were targeted for “their support to China’s military modernisation efforts, specifically the People’s Liberation Army’s aerospace programmes including airships and balloons”, the US Bureau of Industry and Security said.
Mr Kirby said the object spotted above Alaska on Thursday night was thought to not have the self-propulsion or manoeuvrability capabilities like the balloon the US downed.
Because it was a smaller object than the Chinese balloon, which was more than 60 metres wide and over 900 kilograms, the object downed on Friday was expected to create a far smaller debris field.
Pentagon spokesman Brig Gen Pat Ryder told reporters that an F-22 fighter aircraft based at Joint Base Elmendorf-Richardson had shot down the object using the same type of missile used to take down the balloon nearly a week ago.
Ahead of the the shoot-down, the Federal Aviation Administration restricted flights over the area on the Beaufort Sea about 160 kilometres from the Canadian border.