Two Chinese spy balloons have been shot down by the US in the last week after they posed a "threat" to civilians.
US President Joe Biden was forced to order a fighter jet to shoot down an unidentified "high-altitude object" off Alaska on Friday.
The object was flying at 40,000ft over the coast of Alaska and had reached speeds of 40mph.
It was travelling towards the North Pole before being shot down.
The White House said the object was "the size of a small car" and posed a "reasonable threat" to commercial flights. The purpose of the object remains unclear.
It is the second time the American military has been ordered to destroy an object in the sky this month after a Chinese balloon was spotted floating over US waters.
The first object was shot down last Saturday in South Carolina after John Kirby, White House National Security Council spokesman, said it posed a "reasonable threat" to the safety of civilian flights.
However, China has rejected claims the objects were part of a spying mission and said they were civilian meteorological balloons that had blown off course.
They added the US had "overreacted" by shooting them down.
First Chinese spy balloon shot down off South Carolina
The first object shot down by US jets was last Saturday after a Chinese spy balloon had been flying over Billings, in Montana, before being shot down off the coast of South Carolina.
The mysterious balloon was ordered by Joe Biden to be shot down amid rising tensions between the US and China.
Eyewitnesses captured the moment the object was shot down as balloon debris was found largely intact on the ocean floor as divers recovered most of the balloon.
The balloon was found to be carrying equipment capable of intercepting communications.
“The high-altitude balloon’s equipment was clearly for intelligence surveillance and inconsistent with the equipment onboard weather balloons,” a senior state department official said.
Second object blown up over Alaska
A second object was ordered to be blown up on Friday after an object the "size of a small car" was spotted over Alaska.
The unknown object was flying at about 40,000ft after a mysterious object had been spotted in the sky.
President Joe Biden ordered the military to shoot down the object, which fell into US waters.
John Kirby, White House National Security Council spokesman, said: "I can confirm that the department of defence was tracking a high-altitude object over Alaskan airspace in the last 24 hours.
“Out of an abundance of caution and at the recommendation of the Pentagon, President Biden ordered the military to down the object, and they did, and it came inside our territorial waters.”
However, Mr Kirby said he is unsure of who owns the balloon.
He added: "We do not know who owns it, whether it's state owned or corporate owned or privately owned."
US believes China behind the balloons
The Pentagon claims the Chinese balloon shot down off the coast of South Carolina on Saturday was part of a large surveillance programme China had been running for "a number of years."
Brigadier General Pat Ryder, the Pentagon press secretary, said in a news conference on Wednesday similar balloons flew over American waters four times during the Trump and Biden administrations.
Secretary of State Antony Blinken cancelled a planned weekend trip to Beijing to deal with the crisis.
Defence Secretary Lloyd Austin called Chinese Defence Minister Wei Fenghe last week to discuss the ballon but he declined to pick up, according to the Pentagon.
However, Chinese officials on Friday hit back and accused the US of "political manipulation and hype".
China rejects US spying claims
China aggressively hit back at the US claims amid concerns the balloons were used for spying.
They said they were going to "take further actions" and criticised the US for "an obvious overreaction and a serious violation of international practice."
In a statement Sunday, China's Ministry of Foreign Affairs said: "China will resolutely uphold the relevant company's legitimate rights and interests, and at the same time reserving the right to take further actions in response."
Balloons fitted with "special surveillance equipment"
The Biden administration says the Chinese balloon shot down over the US last week had been fitted with specialist surveillance equipment capable of collecting intelligence signals.
The balloon is part of an enormous aerial programme linked to Beijing's military and has targeted over 40 countries.
According to the defence secretary the objects were taken to "labs for subsequent analysis."
Just last year five Chinese companies were added to the US government's trade blacklist amid concerns of their support for military aerospace programmes.
Similar objects may have floated over UK
UK Defence Secretary Ben Wallace said it was highly likely that a similar balloon may have floated over Britain which was used to collect information from below.
Mr Wallace said it was "not unusual" for satellites to go through UK skies as they have done so for many years.
He said: "Is it the case that a Chinese satellite has probably circled Britain and looked at us? “I should think yes.’”
Is it a breach of security?
President Biden said the balloons did not represent a major breach of security.
However, any object that comes into their airspace, the US has the right to do what they want, he added.
Mr Biden said: "It's not a major breach. I mean, look ... it's a violation of international law. It's our airspace. And once it comes into our space, we can do what we want with it."
Republicans had criticised Biden for not acting sooner to down the balloon.
