WASHINGTON (Reuters) -The U.S. military shot down on Sunday an octagonal object over Lake Huron near the Canadian border, U.S. officials said, the fourth object downed this month as North American security forces have been on high alert for airborne threats.

Two U.S. officials, speaking on condition of anonymity, told Reuters that 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 U.S. official said the object had an octagonal structure with no discernable 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 U.S. airspace, the official said.