Large drones have been spotted over New Jersey and New York City in recent weeks – but no one knows who is operating them.

The drones reportedly measure 6 feet in diameter and were seen flying at night, sometimes without lights, causing concern among residents and officials.

They were spotted for the first time last month near the Picatinny Arsenal, a U.S. military research and production facility, and over President-elect Donald Trump’s golf course in New Jersey.

There have been dozens of night flights since then and the number of sightings has increased in recent days, although officials say some of the objects seen may have been aircraft rather than drones.

The FBI is investigating and has asked residents to share any videos, photos and other information they may have.

The drones were predominantly seen in New Jerseywith some also spotted in New York City and parts of Pennsylvania, including over Philadelphia.

Despite the national interest, authorities have stressed that the drones do not appear to pose a public safety problem.

Following a briefing by the Department of Homeland Security (DHS) on Wednesday, New Jersey Rep. Dawn Fantasia said she was told that the devices do not appear to be flown by hobbyists, particularly because they are much larger than the devices which are normally used by occasional flyers.

Republican Rep. Erik Peterson, who attended Wednesday’s DHS briefing, said they appeared to have “no idea” who was behind the flying objects.

Two Republican congressmen from the Jersey Shore area – Reps. Chris Smith and Jeff Van Drew – have called on the military to shoot down the drones, with the latter claiming on Fox News that they were coming from an “Iranian mothership.”

But Pentagon spokeswoman Sabrina Singh told reporters Wednesday that “our initial assessment here is that these are not drones or activity emanating from a foreign entity or adversary.”

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Drones are legal in New Jersey for recreational and commercial use, but they are subject to local Federal Aviation Administration (FAA) regulations and flight restrictions and operators must be FAA certified.

Many local politicians called for greater restrictions on eligibility to fly the unmanned devices, with some suggesting a temporary ban on drone flights in the state.

James Edwards, a resident of Succasunna, New Jersey, told The Associated Press that he has seen some drones flying over his neighborhood since last month.

“It’s particularly concerning because there’s so much that’s unknown,” he said. “There are a lot of people talking about various conspiracies that they believe are at play here, but that just adds unnecessary fuel to the fire. We have to wait and see what really happens here and not let the fear of the unknown overwhelm us.”

New Jersey Gov. Phil Murphy said earlier this week that they were taking the issue “dead seriously,” adding, “I don’t blame people for being frustrated.”