The US military has shot down an octagonal object over Lake Huron near the Canadian border, the fourth object downed this month as North American security forces have been on high alert for airborne threats.

Two US officials, speaking on condition of anonymity, said the military had shot down the object but declined to say whether it resembled the large white Chinese balloon that was shot down earlier this month.

A senior US official said the object had an octagonal structure with no discernible payload, a senior administration official said on condition of anonymity.

The United States has no indication the object posed a military threat or had surveillance capabilities.

The object was recently detected over Montana, prompting the closure of US airspace, the official said.

This marks the fourth unidentified flying object that has been destroyed over North America this month, straining US relations with China.

Officials said the latest object was shot down using a Sidewinder missile in US airspace at an altitude of 20,000 feet (6100m), where it could have potentially interfered with domestic air traffic.

US Representative Elissa Slotkin, who represents a district in Michigan near where the incident took place, said pilots from the US Air Force and National Guard shot down the object. “Great work by all who carried out this mission,” she wrote on Twitter.

The first object was a balloon shot down off the coast of South Carolina on February 4.

On Friday, a second object was shot down over sea ice near Deadhorse, Alaska. A third object was destroyed over Canada’s Yukon on Saturday, with investigators still hunting for the wreckage.

“Recovery teams are on the ground, looking to find and analyse the object,” Prime Minister Justin Trudeau told reporters on Sunday.

“The security of citizens is our top priority and that’s why I made the decision to have that unidentified object shot down,” he said, adding that it had posed a danger to civilian aircraft.

North America has been on high alert for aerial intrusions following the appearance of a white, eye-catching Chinese airship over American skies earlier this month.

That 60-metre-high balloon – which Americans have accused Beijing of using to spy on the United States – caused an international incident, leading Secretary of State Antony Blinken to call off a planned trip to China only hours before he was set to depart.

Surveillance fears appear to have US officials on high alert.

Twice in 24 hours, US officials closed airspace – only to reopen it swiftly.

On Sunday, the Federal Aviation Administration briefly closed space above Lake Michigan. On Saturday, the US military scrambled fighter jets in Montana to investigate a radar anomaly there.

China denies the first balloon was being used for surveillance and says it was a civilian research craft. It condemned the United States for shooting it down off the coast of South Carolina last Saturday.

US Senate Majority Leader Chuck Schumer told US broadcaster ABC that officials think two of the latest objects were smaller balloons than the original one.

The White House said only that the recently downed objects “did not closely resemble” the Chinese balloon, echoing Schumer’s description of them as “much smaller.”

Canadian counterparts trying to piece together what was shot down over the Yukon may have their own challenges.

The territory is a sparsely populated region in Canada’s far northwest, which borders Alaska. It can be brutally cold in the winter, but temperatures are unusually mild for this time of year, which could ease the recovery effort.