There was no comment by the Pentagon on the situation. (File)
The airspace over Lake Michigan has been temporarily restricted due to national defence reasons, according to a U.S. Federal Aviation Administration notice on Sunday.
The notice said the airspace was being restricted for "national defense" reasons. There was no immediate comment from the Pentagon or the FAA.
The closure of the airspace follows the shoot-down by U.S. aircraft of a Chinese spy balloon and two unidentified flying objects.
Canadian investigators are hunting for the wreckage of the mysterious flying object shot down by a U.S. fighter jet over Yukon territory, Prime Minister Justin Trudeau said Sunday, as the U.S. Senate's top lawmaker said that it - and another flying object shot down off the coast of Alaska - both appeared to be balloons.
"Recovery teams are on the ground, looking to find and analyze the object," Trudeau told reporters. He gave no hint as to what it was but said it "represented a reasonable threat to the security of civilian flight."
"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.
U.S. Senate Majority Leader Chuck Schumer provided a bit more detail to U.S. broadcaster ABC, saying that American national security officials believe the object destroyed over Canada - as well as another flying object shot over the sea ice near Deadhorse, Alaska on Friday - were both balloons.
"They believe they were (balloons), yes, but much smaller than the first one," Schumer said, referring to the balloon that was shot down off the coast of South Carolina last Saturday - a big, white, eye-catching inflatable whose trip across the U.S. airspace at the beginning of the month sparked an international incident.
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."
American officials have accused the Chinese of using the 200-foot-tall (60-meter-high) balloon for surveillance. China's government has said it was a civilian research vessel that went off course and has condemned its destruction.
U.S. officials have been scouring the ocean to recover debris and electronic gadgetry since the original balloon's destruction. Schumer said he was confident U.S. investigators would get to the bottom of what it was being used for.
"We're going to probably be able to piece together this whole, whole surveillance balloon and know exactly what's going on," he said.
Meanwhile North America is on high alert for aerial intruders.
On Saturday, the U.S. military also scrambled fighter jets in Montana to investigate a radar anomaly that triggered a brief federal closure of airspace. North American Aerospace Defense Command (NORAD) later said the pilots didn't identify anything corresponding to the radar hits.
Republican lawmaker Mike Turner, who serves on the U.S. House Armed Services Committee, suggested that President Joe Biden's administration might be overcompensating for what he described as its previously lax monitoring of American airspace.
"They do appear somewhat trigger-happy," Turner told CNN on Sunday.
"I would prefer them to be trigger happy than to be permissive."
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)