The US military is unaware of the identity of the three flying objects it blasted over North America and how they managed to stay in the air.
On Sunday, President Joe Biden issued a new order to bring down another item, making a total of four this month.
The US claimed that because it was flying at 20,000 feet (6,100 meters), it might have hampered commercial air travel.
It may be a “gaseous type of balloon” or “some type of propulsion system,” according to a military commander.
China claims that the US deployed over 10 balloons into their airspace.
Aliens might still be responsible for the objects, he noted.
Defence officials have called the most recent object, which was shot down over Lake Huron in Michigan close to the Canadian border, an unmanned “octagonal construction” with strings attached.
At 14:42 local time, a missile launched from an F-16 fighter jet brought it down (19:42 GMT).
Further doubts are raised by the occurrence regarding the recent spate of high-altitude objects that have been shot down over North America.
General Glen VanHerck, commander of US Northern Command, stated that there was no sign of any threat.
“They won’t fall under the balloon category, I’m afraid. For a reason, we’re naming them objects, “explained he.
He continued, “What we are seeing are really little things that have an extremely low radar cross-section.
In recent days, speculation over what the objects might be has been more intense.
When asked if it was possible that the objects were aliens or extra-terrestrials, Gen. VanHerck replied, “I will let the intelligence community and the counterintelligence community sort it out.”
“At this time, I haven’t ruled anything out.”
After circling the US for several days, a suspected Chinese spy balloon was shot down off the coast of South Carolina on February 4. According to officials, it was developed in China and deployed to keep an eye on critical websites.
China claimed the object was a weather monitoring equipment that had gone awry and denied it was used for surveillance. Tensions between Washington and Beijing increased as a result of the incident and the heated discussions that followed.
But on Sunday, a defense official claimed that the US had spoken to Beijing about the first object after waiting for several days for a response. What was being discussed was not immediately obvious.
American fighter jets had shot down three additional high-altitude objects in as many days since the initial incident.
On Friday, President Biden gave the order to shoot down an item over northern Alaska, and on Saturday, another similar object was also shot down over the Yukon in western Canada.
The search in Alaska has been constrained by arctic circumstances, but both the US and Canada are actively seeking to recover the debris.
A representative for the White House National Security said, “These objects did not closely resemble, and were considerably smaller than, the [4 February] balloon, and we will not be able to characterize them with certainty until we can recover the wreckage.”
The US has flown balloons into Chinese airspace more than ten times in the last year, according to a report from China’s foreign ministry on Monday.
The US frequently violates other nations’ airspace, according to Wang Wenbin, the foreign ministry’s spokeswoman, during a press conference.
A US official told the Washington Post on Saturday that broadening the scope of the radar and sensor search could lead to the discovery of the most recent objects.
The official, who asked to remain anonymous, compared it to a vehicle buyer unticking boxes on a webpage to expand the search criteria.
But he added that it wasn’t obvious if this was causing more hits or if the recent invasions were a result of a more planned attack.
Timeline for unidentified flying objects
4 February: A suspected surveillance balloon is shot down by the US military off the coast of South Carolina. According to officials, it came from China and had been observing vital sites as it hovered over the US for days.
10 February: The US shoots down another item off the coast of northern Alaska, according to officials, which had no propulsion or control systems.
On February 11, about 100 miles (160 km) from the US border, an American fighter jet shoots down a “high-altitude flying object” above Canada’s Yukon territory. The second balloon was said to be smaller and cylindrical.
12 February: “Out of an abundance of caution,” US jets fire down a fourth high-altitude object near Lake Huron.
Objects downed above the North American airspace boundary are shown on a map.
According to a senior officer, the three most recent items that were fired down were probably weather instruments rather than surveillance balloons.
The top Democrat in Congress, however, who earlier informed the broadcaster that intelligence agencies suspected the items were actually surveillance balloons, appeared to contradict this.
Senate Majority Leader Chuck Schumer said, “These believe they were [balloons], yeah. They were significantly smaller than the first one shot down off the South Carolina coast.”
“What’s gone on the last two weeks or so… has been nothing short of madness,” Democratic Senator Jon Tester of Montana told the BBC’s US partner CBS.
Republicans have criticized the Biden administration for handling the first suspected spy balloon on several occasions, claiming it should have been shot down far earlier.
In case an object is found in their airspace, other nations are intently observing the US’s response.
Prime Minister Rishi Sunak of the UK promised to do “everything it takes” to keep the nation secure.
As he said, “We have something called the quick reaction alert force, which incorporates Typhoon jets, and which is kept on 24/7 readiness to police our airspace, which is really crucial.”