WASHINGTON: The United Nations in a 4th, shot down another flying object on Sunday, this time over Lake Huron on the US-Canadian border.

President Joe Biden ordered a F-16 fighter to shoot down the latest object- an octagonal structure with strings hanging off it “out of abundance of caution,” a senior administration official said.

Though it did not deemed to be a military threat to anything on the ground, but it could have posed a hazard to civil aviation as it flew at about 20,000 feet (6,000 meters) over Michigan, the official said.

Reflecting the heightened state of alert, US authorities briefly closed the airspace over Lake Michigan Sunday, before the latest object was shot down further towards the Canadian border.

The US aerospace command NORAD tracked the new object visually and with radar, and it was downed over the lake “to avoid impact to people on the ground while improving chances for debris recovery,” the Pentagon said in a statement.

Meanwhile Canadian Prime Minister Justin Trudeau was heading Sunday to the western Yukon territory, where the third unidentified object was shot down a day earlier. There, a US F-22 jet, acting on orders from the prime minister and US President Joe Biden, downed a “high-altitude airborne object” about 100 miles (160 kilometers) north of the border.

Canadian officials described it as small and cylindrical, roughly the size of a Volkswagen car. Recovery teams backed by a Canadian CP-140 patrol aircraft were continuing their search Sunday for debris in the Yukon, officials said.

Canadian investigators are hunting for the wreckage of the mysterious flying object shot down over Yukon territory, Prime Minister Justin Trudeau said Sunday. He gave no hint as to what it was but said it “represented a reasonable threat to the security of civilian flight.”