Pentagon officials on Sunday (local time) said they have been scrutinizing radar more closely since the sightings of unidentified objects and have not been able to identify what the most recent objects are, or how long they are staying aloft.

In a press briefing, Air Force General Glen VanHerck, who safeguards US airspace as head of North American Aerospace Defense Command (NORAD) and Northern Command, said, “We’re calling them objects, not balloons, for a reason.” He said that Pentagon does not know what keeps these “objects” aloft, unknown propulsion systems.

The military will try to recover the object downed over Lake Huron, which they said likely fell in Canadian waters, to learn more about it, VanHerck told reporters.

Pentagon and intelligence officials are trying to make sense of three unidentified flying objects over Alaska, Canada and Michigan that US fighter jets shot down with missiles on Friday, Saturday and Sunday.

Meanwhile, an unidentified object was shot down over the Great Lakes region Sunday at the direction of President Joe Biden.

“Today at 2:42 p.m. ET, at the direction of President Biden, and based on the recommendations of Secretary Austin and military leadership, an F-16 fired an AIM9x to successfully shoot down an airborne object flying at approximately 20,000 feet altitude in US airspace over Lake Huron in the State of Michigan,” read North American Aerospace Defense Command statement.

The object was shaped like an octagon with strings hanging off it and did not appear to be carrying anything. It was shot down by US F-16 fighter jets on Sunday and was flying at 20,000 feet over Michigan’s Upper Peninsula. It was about to go over Lake Huron when it was neutralized.

Military officials believe the object shot down over Lake Huron on Sunday is likely the same object that was spotted over Montana on Saturday, said VanHerck.

He told reporters that the object shot down Sunday was first spotted around 4:45 ET on Saturday afternoon. He scrambled F-15 fighters and a KC-135 tanker to go investigate, and the object crossed into US airspace a few hours later, he said.

“It’s likely, but we have not confirmed, that the track that we saw in Wisconsin was likely the same track in Montana,” VanHerck said.

“We monitored the track of interest as it passed over Lake Michigan. We assessed that it was no threat, physical threat, military threat … to critical infrastructure. That’s my assessment and continues to be today,” he added.

The operation marks the third day in a row that an unidentified object was shot down over North American airspace. An unidentified object was shot down over northern Canada on Saturday. On Friday, an unidentified object was shot down in Alaska airspace by a US F-22. Last weekend, a suspected Chinese surveillance balloon was taken down by F-22s off the coast of South Carolina.

Notably, the US military has not yet recovered the object shot down over Alaska on Friday. “We’re actively searching for that object right now. I’ve got a Navy P-8, which is surveilling the area, with helicopters as well. Once we locate that object, we’ll put an Arctic security package in there and begin the analysis and recovery, but we don’t have it right now,” VanHerck said.

He also said that the country of origin, shape or mechanics of the three latest objects downed cannot be confirmed.

“I would be hesitant and urge you not to attribute it to any specific country. We don’t know,” VanHerck said