WASHINGTON, United States, (AFP) – A US warplane shot down another flying object on Sunday, this time over Lake Huron on the US-Canadian border, the fourth in a dramatic series that began with the downing of a suspected Chinese spy balloon a week ago.

Jittery Americans have been watching the skies as the mysterious incursions unfolded against a backdrop of acute tensions with China — although only the first object has so far been attributed to Beijing.

President Joe Biden ordered a F-16 fighter to shoot down the latest object “out of abundance of caution,” a senior administration official said.

This new device — described as an octagonal structure with strings hanging off it — was 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.

“We have no indication that it has surveillance capabilities but nor can we rule that out,” the official said on condition of anonymity.

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.

A senior Republican on Sunday accused Beijing of “an act of belligerence” regarding the first object, a Chinese balloon shot down February 4 off the US East Coast after American officials said it was engaged in spying.

China has insisted it was a weather balloon blown off course.

“It was done with provocation to gather intelligence data, and collect intelligence on our three major nuclear sites,” Michael McCaul, chairman of the House Foreign Affairs Committee, told CBS.

US Senate Majority Leader Chuck Schumer, among senior lawmakers who received a government briefing, told ABC the second and third objects — one shot down over Canada’s Yukon territory on Saturday, and one downed over Alaska on Friday — both appeared to be balloons, but “much smaller than” the first large one.

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.

US teams were struggling with Arctic conditions as they searched near Deadhorse, Alaska, where the second object was shot down Friday.

Operations were also continuing off the South Carolina coast, where the past week’s drama climaxed when the initial large balloon was shot down.