US aviation authorities have announced a temporary ban on the use of drones in nearly two dozen cities of New Jersey until mid January.

But mystery continues to swirl after nearly a month of drone sightings over New Jersey and other US states, alarming some residents.

Authorities have been unable to provide definitive answers about these sightings, saying only that the flying objects are not believed to pose a danger to the public or national security.

On Sunday, Homeland Security Secretary Alejandro Mayorkas confirmed the sightings included drones, as well as manned aircraft commonly mistaken for drones.

He added that he knows of "no foreign involvement" to do with the unmanned aerial vehicles.

Some lawmakers have criticised the government's handling of the drone reports and the lack of public information.

The drone reports have prompted a wide-range of baseless conspiracy theories, including that they are searching for nuclear weapons, radioactive "dirty bombs" or are form part of an impending invasion by aliens.

Here's what we know.

Where have drones been spotted?

Dozens of drone sightings have been reported over New Jersey since 18 November, but others have been reported around the US north-east.

Some of the flights were spotted near Picatinny Arsenal - a sensitive military research facility - as well as near President-elect Donald Trump's golf course in the town of Bedminster, New Jersey.

The Federal Aviation Administration (FAA) has since issued temporary restrictions prohibiting drone flights over 22 cities including Bedminster and Picatinny until 17 January.

Sightings have also been reported in several other states:

1. In New York City, several drones were reported flying over the Bronx on 12 December
2. Stewart Airfield in New York state had to shut down for about an hour on 13 December because of drone activity, Governor Kathy Hochul said
3. In Connecticut, police confirmed "suspicious drone activity". A drone detection system is now in use near the towns of Groton and New London
4. In Maryland, former Republican Governor Larry Hogan said he saw what appeared to be "dozens" of drones over his home in Davidsonville
5. In Massachusetts, two men were arrested on 14 December after a "hazardous drone operation" near Logan International Airport's airspace in Boston, police said
6. Multiple sightings have been reported in eastern Pennsylvania, including over Philadelphia
7. In October, the Wall Street Journal reported that mysterious drones were seen for 17 days near US military facilities in Virginia
8. In Ohio, a US Air Force base was briefly closed on 13 December after small drones were detected flying nearby. More drones were reported on 16 and 17 December, although the airbase's operations were not impacted

In late November, drones were also spotted over three US airbases in the UK, with British defence sources telling the BBC suspicion had fallen on a "state actor".

Drones were also reported near the Ramstein US military airbase in Germany in early December.

What have investigators said about the drones?

US President Joe Biden has said that there is "nothing nefarious" about the drone sightings, and "no sense of danger".

In an earlier call with reporters, officials from several US agencies said there was no evidence of any threat to public safety.

"I think there has been a slight overreaction," an official from the FBI said.

The homeland security secretary told ABC News on Sunday he knows of "no foreign involvement with respect to the sightings in the north-east".

"And we are vigilant in investigating this matter," he said.

Mayorkas added: "If there is any reason for concern, if we identify any foreign involvement or criminal activity, we will communicate with the American public accordingly."

Following a closed-door briefing on 17 December, Connecticut representative Jim Himes said that senior defence and law enforcement officials had told lawmakers that "there is zero evidence of laws being broken" by the drones.

He added that the "vast majority" of sightings were normal aircraft or drones being operated lawfully.

Himes said that "millions" of unregistered drones were operating across the US, in addition to 800,000 registered drones that weigh more than half a pound.

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