The US shot down an unidentified object flying close to military bases over Lake Huron in Michigan on Sunday (12 February).
The takedown marked the fourth in a week after objects were shot down in Alaska and Canada on Friday and Saturday.
Under president Joe Biden's orders, the military downed the octagon-shaped "object" using an F-16 fighter jet missile at around 2.42pm. The object was flying at an altitude of 20,000ft.
Teams are trying to recover the object from the lake.
"We are calling them objects, not balloons, for a reason," US Air Force General Glen VanHerck told the media.
The US military said they had not seen any evidence of the objects being extraterrestrial, but said they were not ruling anything out.
"I’ll let the intel community and the counterintelligence community figure that out," VanHerck said when asked whether it could be a UFO.
"I am not able to categorise how they stay aloft. It could be a gaseous type of balloon inside a structure or it could be some type of propulsion system. But clearly, they’re able to stay aloft."
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It comes after a string of other objects were taken down over the past week alone.
On 4 February, a suspected Chinese spy balloon off the Carolina coast was shot down.
This was followed by a "car-sized object" shot down over sea ice near Deadhorse, Alaska on 10 February.
On 11 February, a third unidentified object was flying over the northern Canadian territory of Yukon with Canada's prime minister Justin Trudeau ordering a US warplane to down it.
Then, on Sunday (12 February), the fourth was shot down over Lake Huron.
"These objects did not closely resemble and were much smaller than the PRC balloon and we will not definitively characterise them until we can recover the debris, which we are working on," a spokesperson for the National Security Council said.
The object "presented as an octagonal structure with strings hanging off but no discernible payload," a US official told reporters.
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