Enigmatic drones spotted flying in the skies over Colorado and Nebraska are making citizens quite uneasy, but local and federal authorities so far have no answers, launching probes into who or what is behind the unmarked craft.

Some 16 of the drones have been seen across northeast Colorado in recent weeks, sheriff's departments in two Colorado counties have confirmed. Though the aircraft have not violated any federal guidelines for flying, Yuma County Sheriff Todd Combs said they’ve nonetheless left residents “very nervous and anxious.”

“People do not like the unknown as it upsets the balance of our lives,” Combs wrote in a lengthy Facebook post on Tuesday, noting that there were “many theories about what is going on,” but no definitive explanation.

“I think we are all feeling a little bit vulnerable due to the intrusion of our privacy that we enjoy in our rural community, but I don't have a solution or know of one right now. All I can say is don't live your life in the fear of the unknown,” the sheriff continued.

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Most of the drones – unarmed and generally non-threatening – have been seen flying in low-altitude “Class G” airspace, which under federal regulations gives a wide berth for small private aircraft to “operate as they see fit,” Combs said. Both the FAA and the US Army also deny that the craft are theirs, according to the Denver Post, though the Pentagon and Air Force did not respond to a request for comment. Beyond that, little else is known.

Several divisions of the Federal Aviation Administration (FAA) are now looking into the drones seen flying over both states, FAA spokesman Ian Gregor told CNN. An FAA investigator is also scheduled to meet with Combs’ department next week to get to the bottom of the mystery.

Colorado Senator Cory Gardner also said he was keeping watch over the situation, tweeting on Tuesday that he had been in contact with FAA officials.

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In the meantime, Combs said: “I would like to reassure you, I am doing the best to get you answers,” also warning residents to refrain from attempting to shoot down the craft while they investigate. Some have taken to Twitter to suggest ways to bring the drones down, but authorities warn their batteries could ignite fires on the ground.

The strange phenomenon comes as the FAA seeks to introduce a new rule requiring most drones to be equipped with remote ID technology, which the agency says will “enhance safety and security by allowing the FAA, law enforcement, and Federal security agencies to identify drones flying in their jurisdiction.” A fairly new but rapidly developing technology, there are now some 1.5 million drones and around 160,000 remote pilots registered with the FAA.

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