US military officials say they are unsure how three unidentified flying objects shot out of the skies of North America had been able to stay aloft.
President Joe Biden ordered another object – the fourth in total this month – to be downed on Sunday.
As it was traveling at 20,000ft (6,100m), it could have interfered with commercial air traffic, the US said.
A military commander said it could be a “gaseous type of balloon” or “some type of a propulsion system”.
He added he could not rule out that the objects were extra-terrestrials.
99 Luftballons …