The US has shot down another unidentified object that it says flew near sensitive military sites and could have been used for spying.

It was downed over Lake Huron in Michigan at 2.42pm local time on Sunday on President Joe Biden‘s orders.

A US F-16 jet fired a missile at about 20,000ft amid concerns that its altitude and flightpath could endanger civilian planes.

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It is the fourth incident in just over a week – and the third in as many days – after objects were shot down in Alaska and Canada on Friday and Saturday,

A senior US official, speaking anonymously, described the latest object as having “an octagonal structure with strings hanging off but no discernible payload”.

Authorities restricted airspace over the lake, near the Canadian border, before both US and Canadian jets were sent to intercept it.

Jets were also scrambled on Saturday after radar detected an object over Montana, but it could not be located and it was thought it could be an error.

However, the signal was picked up again by North American Aerospace Defense Command (NORAD) on Sunday, 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,” said a statement.

“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.”

Teams are trying to recover the object from the lake.

US Air Force general Glen VanHerck admitted he did not know what the last three objects shot down were or how they stay aloft.

However, he told reporters they were not the same as the Chinese “spy” balloon downed near South Carolina a week ago.

“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.

A National Security Council spokesperson earlier on Sunday said the unidentified objects shot down over Alaska and Canada were “much smaller” than the Chinese balloon.

‘Object was cylindrical’

Canadian Prime Minister Justin Trudeau said teams were searching for the object shot down over his country.

A US F-22 stealth jet brought it down on Saturday over the sparsely populated Yukon territory in the northwest.

“Recovery teams are on the ground, looking to find and analyse the object,” Mr Trudeau told reporters.

“There’s still much to know about it. That’s why the analysis of this object is going to be very important.”

Canada’s defence minister Anita Anand described it as cylindrical but smaller than the Chinese balloon.

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It was flying at 40,000ft and posed a risk to civilian planes when it was brought down about 100 miles from the border at 3.41pm EST (8.41pm GMT), said Ms Anand.

The Pentagon said NORAD had spotted the object over the coast of Alaska late on Friday.

Jets were scrambled from the Joint Base Elmendorf-Richardson and joined by Canadian CF-18 and CP-140 aircraft after the object crossed the border.

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The Pentagon said the US F-22 shot down the object using an AIM 9X missile “following close coordination” between the countries.

Mr Trudeau said the military would recover the wreckage and that he had spoken to President Biden and thanked NORAD for “keeping the watch over North America”.

Meanwhile, Defence Secretary Ben Wallace has said the UK will conduct a security review following the latest development.

He said: “The UK and her allies will review what these airspace intrusions mean for our security. This development is another sign of how the global threat picture is changing for the worse.”

Earlier this week, Beijing admitted that the balloon shot down off South Carolina had come from China but insisted it was a “civilian airship”.

It said it had strayed into US airspace and was for meteorological and other scientific research.