US aviation authorities have banned the use of drones in 22 cities of New Jersey until 17 January, allowing the government to use "deadly force" against unmanned aircraft if they pose an "imminent security threat".

Pilots operating in restricted zones risk being intercepted and detained by law enforcement, the Federal Aviation Administration said in a statement.

The move comes after weeks of mysterious drones sightings across New Jersey and other states, leading to concern from residents and prompting a number of conspiracy theories online about foreign involvement.

Authorities have not given many definitive answers, but President Joe Biden said the drone sightings were "nothing nefarious".

The order says no unmanned aircraft can operate below 400 feet, the maximum altitude for recreational drone operations under FAA rules.

Several of the restricted zones are around infrastructure, like power substations. Others cover areas like port and airspace around military installations, or airports.

The FAA says a handful of agencies, such as law enforcement and disaster response missions, are not included in the restrictions,.

Some commercial drone operations will be permitted under the restrictions, but operators will need a valid statement of work and an approved special governmental interest airspace waiver.

For weeks, Americans have been reporting drones flying near American military bases, close to coastlines and around US infrastructure.

The Pentagon earlier denied the suggestion of one New Jersey lawmaker that the possible drones came specifically from an Iranian "mothership", while an FBI official said there may have been "a slight overreaction" on the topic.

"We're following this closely, but so far, no sense of danger," President Biden said on Wednesday.

Following a US House Intelligence Committee closed-door briefing on Tuesday, members of congress tried to reassure the same.

The "vast majority" of sightings were normal aircraft or drones being operated lawfully, Connecticut Representative Jim Himes said.

As the mystery persists, state governments are calling for more power to deal with the small, uncrewed aircraft being spotted in the skies. Earlier this week, New York Governor Kathy Hochul said officials were sending her a drone detection system.

Among those who have voiced their suspicions are President-elect Donald Trump, who has said the government "knows what it happening", but "for some reason they don't want to comment". However, he said he "can't imagine it's the enemy".