US fighter jets have now shot down four flying objects in fewer than 10 days.

The latest instance, involving what US officials described as an “unidentified” object, was brought down near the US-Canada border on Sunday on the orders of President Joe Biden.

It comes after the military downed the first flying object, a suspected Chinese “spy” balloon, off the Carolina coast on 4 February.

Two other objects were also shot down, on 11 February and 12 February.

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.

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.

The object sparked a diplomatic row between the US and China, with US Secretary of State Anthony Blinken postponing his planned trip to Beijing at short notice.

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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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.

“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.

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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.

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“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.