Though Beijing has confirmed the first was from China, US officials are yet to give further details about the nature of the three latter objects, which so far remain unidentified.
Here, Sky News takes a look at when and where the four objects were shot down, and what we know so far.
4 February
The first object, described by US officials as a suspected Chinese “spy” balloon, was first spotted by US air defence systems flying towards Alaska from the Bering Sea.
The balloon moved through Canada before dipping back into the US and out off the coast of South Carolina, where it was shot down with a missile fired by an F-22 fighter aircraft, about six nautical miles off the coast near Myrtle Beach.
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A US defence official said the aircraft was a spy balloon and that China had intended to use it on sensitive military sites.
However, China insisted the balloon was used for meteorological and other scientific research and had been blown off course.
In a statement, the Chinese Foreign Ministry called the shooting down of the balloon an “obvious overreaction” that “seriously violated international conventions”.
10 February
A second object, described as being “about the size of a small car” was spotted by the North American Aerospace Defense Command (NORAD) near Alaska and downed on 10 February.
According to Pentagon press secretary Brigadier General Patrick Ryder, the object, which was hovering at an altitude of around 40,000ft, was “not similar in size or shape” to the balloon shot down off South Carolina.
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Unknown object shot down by US was ‘size of small car’
Two US F-22 warplanes were dispatched from Joint Base Elmendorf-Richardson near Anchorage, Alaska, and the object was shot down over sea ice near Deadhorse.
US officials said a search team had been sent to recover debris from the object in order to identify what it is and where it had come from.
11 February
A third object, again unidentified but described by US officials as “much smaller” than the suspected spy balloon, was tracked entering US airspace over Alaska before drifting over Canada.
Canadian officials described the object, which was flying at an altitude of around 40,000ft, as “small” and “cylindrical” and that it “posed a reasonable threat”.
Again, US F-22 jets tracked the object, while Canadian CF-18 fighters and CP-140 maritime patrol craft also joined the operation.
The object was shot down by a US F-22 over a central area of Canada’s Yukon Territory, on the orders of Canadian Prime Minister Justin Trudeau.
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The object was shot down by a US F-22 fighter jet.
“To our knowledge, this is the first instance of Norad downing an object in Canadian airspace, and the importance of this moment should not be underestimated,” said Canada’s Defence Minister Anita Anand.
12 February
On Sunday, US officials confirmed another unidentified object had been shot down by fighter jets over Lake Huron on the US-Canada border near Michigan.
This time the object was flying at a considerably lower altitude, around 20,000ft.
It was shot down by an F-16 jet, on the orders of Mr Biden, due to concerns that its altitude and flight path could endanger civilian planes.
A senior US official, speaking anonymously, described the latest object as having “an octagonal structure with strings hanging off but no discernible payload”.
In a statement, the Pentagon said: “Based on its flight path and data we can reasonably connect this object to the radar signal picked up over Montana, which flew in proximity to sensitive DOD [Department of Defense] sites.
“We did not assess it to be a kinetic military threat to anything on the ground, but assess it was a safety flight hazard and a threat due to its potential surveillance capabilities.”
US Air Force general Glen VanHerck admitted he did not know what the last three objects shot down were or how they stayed aloft.
However, he told reporters they were not the same as the Chinese “spy” balloon.
“We’re calling them objects, not balloons, for a reason,” he said – also refusing to rule out any explanation when asked if they could be extra-terrestrial.
Bodycam footage showing prison officers fatally beating an inmate has been released by New York’s attorney general.
Prison officers at Marcy Correctional Facility in New York punched and kicked 43-year-old Robert Brooks repeatedly while he was handcuffed on an infirmary bed.
He died in hospital on 10 December, a day after the attack.
The incident has drawn outrage from political leaders and was condemned by the prison officers’ union as “incomprehensible”, according to Sky News’ partner newsroom NBC.
It is now being investigated by state attorney general Letitia James, who called the videos “shocking and disturbing” at a virtual news conference.
In the video, Mr Brooks is in handcuffs as he is carried into the infirmary by several prison guards.
They put him on the bed and begin repeatedly punching and kicking him.
He is pulled upright, where his bloodied face is visible on camera, and then yanked from the bed by his shirt collar and pushed up against a window.
One of the fourteen workers involved in the incident has resigned and the rest have been suspended without pay until the process to fire them is complete. The workers include correctional officers, sergeants and a prison nurse.
The officers had not activated their body cameras but they were still on and recorded in standby mode, without audio, during the attack.
As a result of the incident, all officers will now need to have their cameras activated any time they are engaging directly with prisoners.
Mr Brooks’ family thanked officials for taking action “to hold officers accountable” in a statement this week.
“We cannot understand how this could have happened in the first place,” the family said. “No one should have to lose a family member this way.”
The attack happened before 9.30pm on 9 December in a medical exam room after Mr Brooks had been transferred from the Mohawk Correctional Facility to Marcy Correctional Facility.
An autopsy found “preliminary findings show concern for asphyxia due to compression of the neck as the cause of death, as well as the death being due to actions of another,” according to a state corrections office investigative report obtained by an affiliate of Sky News’ partner newsroom WKTV in Utica.
Mr Brooks had been behind bars since 2017 on a 12-year sentence for first-degree assault involving a longtime girlfriend.
Officials declined to say why he had been transferred to the Marcy Correctional Facility, a medium-security prison.
Last year, an independent prison oversight group called The Correctional Association of New York released a report on the Marcy Correctional Facility.
It noted complaints of “rampant” physical abuse by staff members, with 80% of incarcerated people reporting having witnessed or experienced abuse and nearly 70% reporting racial discrimination or bias.
In response to the video, the union that represents workers at the prison said: “What we witnessed is incomprehensible to say the least and is certainly not reflective of the great work that the vast majority of our membership conducts every day.”
It adding what transpired is the “opposite of everything [the union] and its membership stand for.”
The world’s best golfer has suffered a freak injury while cooking Christmas dinner, forcing him to undergo surgery.
Scottie Scheffler sustained a puncture wound after cutting the palm of his right hand on broken glass.
The world number one required surgery as small glass fragments remained in the palm after the accident.
The injury has forced him out of the first tournament of the season, next week’s The Sentry in Hawaii.
But the 28-year-old has been told he will recover in three to four weeks, and he hopes to be back in action at The American Express tournament in California on 16 January.
Scheffler won an Olympic gold and seven PGA Tour titles in the last year and was recently named PGA Tour’s Player of the Year for a third season in a row.
In May, he was arrested by police during the US PGA Championship after he was accused of trying to drive around a traffic jam caused by a fatal accident.
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Just hours later, he was released and allowed to return to Valhalla Golf Club in Kentucky to play his second round of the tournament.
Criminal charges against Scheffler were later dismissed due to a lack of evidence and a police officer who arrested him was disciplined for not having his bodycam on at the time of the incident.
The man accused of burning a woman to death on a New York subway train has been indicted on murder and arson charges.
Sebastian Zapeta is accused of setting a sleeping woman on fire and then fanning the flames with a shirt, which caused her to be engulfed by the blaze.
He allegedly sat on a platform at Brooklyn’s Coney Island station, opposite the stopped train, and watched as she burned to death.
Authorities are still working to identify the victim.
Zapeta, 33, has been charged with one count of first degree murder, two counts of second degree murder and one count of arson in the first degree.
After a brief hearing in which the indictment was announced, Brooklyn District Attorney Eric Gonzalez said: “This was a malicious deed. A sleeping, vulnerable woman on our subway system.”
Mr Gonzalez said police and medical examiners are using fingerprints and advanced DNA techniques to identify the victim, while also retracing her steps before the murder.
“Our hearts go out not only to this victim, but we know that there’s a family,” he said. “Just because someone appears to have been living in the situation of homelessness does not mean that there’s not going to be family devastated by the tragic way she lost her life.”
Such filings are often a first step in the criminal process because all felony cases in New York require a grand jury indictment to proceed to trial, unless a defendant waives that requirement.
Zapeta was not present at the hearing. The most serious charge he is facing carries a maximum sentence of life in prison without parole and the indictment will be unsealed on 7 January.
Zapeta is a Guatemalan who entered the US illegally having already been deported in 2018, officials say.
He was taken into custody last Sunday, after three children called 911 when they recognised him from an image shared by police.
During questioning, prosecutors say he claimed not to know what happened, and noted he consumes alcohol – but did identify himself in photos and videos showing the fire being lit.