Wright-Patterson Air Force Base temporarily closed its airspace late Friday night and early Saturday morning due to the presence of small unmanned aircraft systems (UAS) near the U.S. Air Force base, which is located close to Dayton, Ohio.

According to Dayton Daily News, Robert Purtiman, a Wright-Patterson Air Force Base spokesman, confirmed on Sunday that small unmanned aircraft systems were observed near the base on Friday night and that the base’s airfield was closed for roughly four hours.

“So far, our leadership has determined that none of the incursions impacted any of our residents, facilities or assets,” Purtiman said. “We’re taking all of that appropriate measures to safeguard the installation and all of our residents.”

Purtiman explained that the number of mysterious unmanned aircraft systems observed near the base “has fluctuated, and they have ranged in sizes and configurations.” The spokesperson added, “Our team continues to monitor the local airspace, and we’re working with local authorities to ensure the safety of our personnel, facilities and assets.”

Asked how often the base has had to close its airfield due to the presence of unmanned aircraft systems, Purtiman said, “First time I’m aware of,” according to Dayton Daily News.

An audio recording shared by The War Zone reveals the Wright-Patterson air traffic control tower’s warning to an aircraft labeled “MedFlight 8” to “use extreme caution” due to “heavy UAS movement on the base.” The audio recording also includes guidance from the air traffic control tower that the base’s airspace would be temporarily closed following the aircraft’s “transition.”

While reports of drones and mysterious unmanned aircraft systems flying over U.S. military bases have circulated in the news over the past few weeks, the Federal Bureau of Investigation and the Department of Homeland Security released a statement last week claiming that there is “no evidence at this time that the reported drone sightings pose a national security or public safety threat or have a foreign nexus.”

On Saturday, a Joint Staff spokesperson confirmed that drones had been spotted flying over two U.S. military installations in New Jersey.

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“We have had confirmed sightings at Picatinny Arsenal and Naval Weapons Station Earle,” the Joint Staff spokesperson said.

The spokesperson told reporters that U.S. military installations can “detect and respond” to drones and that U.S. security personnel are trained to identify drones and prevent them from flying unauthorized over military bases.

“To date, we have no intelligence or observations that would indicate that they were aligned with a foreign actor or that they had malicious intent,” the spokesperson stated. “But … we don’t know. We have not been able to locate or identify the operators or the points of origin.”