Defense Secretary Lloyd Austin addressed questions Monday about what exactly is happening in the skies over the United States following the shooting down of various unidentified objects over the weekend. 

"While authorities don't yet know what the objects are, they are not a threat, Austin said. 

"They do not present a military threat to anyone on the ground," he added. "They do however present a risk to civil aviation and potentially an intelligence collection threat. And we'll get to the bottom of it."

Photos taken in Aynor, SC of the Chinese spy balloon shot down. (WHD News)

The U.S. has shot down four objects over North America in the past week, with the first being a Chinese spy balloon off the coast of South Carolina on Feb. 4. The second and third are believed to have been smaller balloons, which were shot down over Alaska and Canada, respectively. Sunday's is the fourth object shot down in about eight days.

The Defense Department (DOD) said President Biden, shortly before 2:42 p.m., directed an F-16 to fire an AIM-9X missile to shoot down an airborne object flying at around 20,000 feet over Lake Huron, Michigan.

Austin said the priority remains debris recovery to "get a better sense of what these objects are." Several federal agencies, including the FBI, Federal Aviation Administration (FAA) and NASA will be working together. Recovery efforts have begun in Alaska, Michigan and South Carolina. 

Efforts in Alaska are especially challenging because the debris land on sea ice, Austin said. American officials are also supporting Canadian recovery efforts in the Yukon Territory where another object crashed landed, he said. 

On Monday, National Security Council spokesman John Kirby reportedly said the Biden administration directed a team to study the policy implications for detection, analysis, and disposition of aerial objects that pose either safety or security risks.

"I know there have been questions and concerns about this but there is no – again, no – indication of aliens or extraterrestrial activity with these recent take-downs," White House Press Secretary Karine Jean-Pierre said during her Monday press briefing.

During his remarks, Austin noted that companies and research groups often operate objects at similar altitudes as the ones shot down for legitimate purposes. He also said the three objects shot down are different from the Chinese spy ballon. 

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 "We knew exactly what that was. A PRC (People's Republic of China) surveillance balloon" Austin said. "We don't know if they (three objects shot down) were actually collecting intelligence but because of the route that they took, out of an abundance of caution, we want to make sure that we have the ability to examine what these things are."

WHD News' Bradford Betz and Kelly Laco contributed to this report.