US aviation authorities have banned the use of drones in 22 infrastructure sites in New Jersey and another 29 in New York state for 30 days after a spike in drone sightings in the eastern US.
The measures allow 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 (FAA) said in a statement.
The move comes after weeks of mysterious drone 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, which initially covered the New Jersey sites, says no unmanned aircraft can operate below 400ft, the maximum altitude for recreational drone operations under FAA rules.
The New Jersey bans will expire on 17 January, but one covering Donald Trump's golf course at Bedminster will continue until 31 January, after his inauguration as president.
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.
Hours after the New Jersey ban was announced, New York Governor Kathy Hochul said similar restrictions would be put in place in her state.
"I've spoken with [Homeland Security] Secretary [Alejandro] Mayorkas multiple times and was just informed that he has coordinated with federal partners and the FAA plans to grant temporary flight restrictions over some of New York's critical infrastructure sites," she said in a statement on Thursday evening.
"This action is purely precautionary; there are no threat to these sites."
Hochul said no public safety or national security threats had been detected but she would seek legislation through Congress to "give states and local law enforcement the authority and resources they need to manage this evolving technology".
The FAA updated its order with the New York sites shortly afterwards. Because these bans were introduced a day later, they will last until 18 January.
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, Hochul said officials were sending her a drone detection system.
Among those who have voiced their suspicions are Trump, who has said the government "knows what is happening", but "for some reason they don't want to comment". However, he said he "can't imagine it's the enemy".
This story originally appeared on BBC News.
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