The Pentagon is monitoring a suspected Chinese "high-altitude surveillance balloon" that has been flying over the United States for a couple of days.
US officials have said the flight path of the balloon could potentially take it over a "number of sensitive sites" and say they are taking steps to "protect against foreign intelligence collection".
Reportedly, fighter jets were mobilised, but US President Joe Biden was advised by military leaders against shooting the balloon out of the sky due to a potential safety threat from the debris.
According to the US Department of Defence, a senior defence official said the US intelligence community has "very high confidence" the balloon belongs to the People's Republic of China.
Pentagon Press Secretary Air Force Brigadier General Pat Ryder said during an impromptu briefing that "the US government, to include NORAD (North American Aerospace Defense Command), continues to track and monitor it closely".
He added: "The balloon is well above commercial air traffic and doesn't pose a threat to civil aviation."
He also said this isn't the first time such a balloon has been seen over the United States.
After the balloon was detected, Brig Gen Ryder said, the US government "acted immediately" to protect against the collection of sensitive information, although he did not detail any of the measures that were taken.
US officials said the object flew over Alaska's Aleutian Islands and then through Canada before the balloon was seen over Montana on Thursday.
The state is home to one of only three nuclear missile silo fields in the country, at Malmstrom Air Force Base.
'Highly likely' balloon is in the intended destination, expert says
With the balloon passing through Canada, an expert believes that there is little chance the flight path above sensitive locations was left to the elements.
Intelligence expert Professor John Blaxland told Forces News that you can, in fact, track wind patterns to "quite a science".
He added: "You can actually track with a degree of fidelity where a balloon path will follow, so, it's highly likely that this is intended to be where it ended up."
He added: "My sense is they know the rough area, and from that level, you can actually surveil quite a lot."
A Chinese Foreign Ministry spokesperson has said that the balloon entered US airspace accidentally, and was, in fact, just used for "mainly meteorological purposes".
According to China's foreign ministry, the alleged spy balloon over the US is just a "civilian airship".
In a statement, a spokesperson said: "It is a civilian airship used for research, mainly meteorological, purposes. Affected by the Westerlies and with limited self-steering capability, the airship deviated far from its planned course.
"The Chinese side regrets the unintended entry of the airship into US airspace due to force majeure".
Force majeure is a common clause in contracts that essentially frees both parties from liability or obligation when an extraordinary event or circumstance beyond the control of the parties prevents one or both parties from fulfilling their obligations.