The US has shot down another unidentified flying object in the fourth military operation of its kind this month.

President Joe Biden ordered it to be downed near Lake Huron, close to the Canadian border, on Sunday afternoon.

The object could have interfered with commercial air traffic as it was traveling at 20,000ft (6,100m), a Pentagon statement said.

It was first detected above military sites in Montana on Saturday, it added.

The object, which was not deemed a military threat, has been described by defence officials as unmanned and octagonal in shape. It was downed by a missile fired from an F-16 fighter jet at 14:42 local time.

The incident raised further questions about the spate of high-altitude objects that have been shot down over North America this month.

A suspected Chinese spy balloon was downed off the coast of South Carolina on 4 February after hovering for days over the continental US. Officials said it originated in China and had been used to monitor sensitive sites.

China denied the object was used for spying and said it was a weather monitoring device that had been blown astray. The incident – and the angry exchanges in its aftermath – ratcheted up tensions between Washington and Beijing.

On Sunday, a defence official said the US had communicated with Beijing about the first object after receiving no response for several days. It was not immediately clear what was discussed.

Since that first incident, American fighter jets have shot down three further high-altitude objects in as many days.

President Biden ordered an object to be shot down over Alaska on Friday, and on Saturday a similar object was shot down over the Yukon in north-western Canada.

Officials have not publicly identified the origin or purpose of these objects. Both the US and Canada are still working to recover the remnants, but the search in Alaska has been hampered by Arctic conditions.

“These objects did not closely resemble, and were much smaller than, the [4 February] balloon and we will not definitively characterise them until we can recover the debris,” a White House National Security spokesperson said.

Unidentified flying objects – timeline

4 February: US military shoots down suspected surveillance balloon off the coast of South Carolina. It had drifted for days over the US, and officials said it came from China and had been monitoring sensitive sites

10 February: US downs another object off northern Alaska which officials said lacked any system of propulsion or control

11 February: An American fighter jet shoots down a “high-altitude airborne object” over Canada’s Yukon territory, about 100 miles (160 km) from the US border. It was described as cylindrical and smaller than the first balloon

12 February: US jets shoot down a fourth high-altitude object near Lake Huron “out of an abundance of caution”

Later on Sunday, the US Air Force general overseeing North American airspace said he had not ruled any explanation out – including extraterrestrial life.

“I’ll let the intel community and the counterintelligence community figure that out. I haven’t ruled out anything,” Gen Glen VanHerck told reporters after being asked about the possibility of aliens.

One senior official told ABC News that the three most recent objects to be shot down were likely weather balloons and not surveillance devices.