Reported mysterious sightings of drone clusters in the night skies over New Jersey and other parts of the northeastern United States have sparked outbursts of frustration among members of Congress and calls for a limited state of emergency to be declared for the region.

Jon Bramnick, a Republican state senator in New Jersey, has called for a ban on all drones until the mystery is solved. ABC’s Action News reported that he called for a “limited state of emergency…until the public receives an explanation regarding these multiple sightings.”

Concern over unexplained drone sightings began in mid-November with isolated posts from residents on social media. The issue has steadily risen up the political food chain and reached the stage of state and federal authorities this week.

On Wednesday, New Jersey Gov. Phil Murphy held a briefing with U.S. Homeland Security Secretary Alejandro Mayorkas as well as congressional and state police officials to discuss the drone reports. He stressed that there was “no known threat to the public at this time.”

Also on Wednesday, the House Subcommittee on Counterterrorism, Law Enforcement and Intelligence held a hearing on the issue. Robert Wheeler, an FBI official assigned to investigate the matter, confirmed at the hearing that the agency still had no explanation for the sightings.

When asked if the public was at risk, Wheeler responded, “Are we concerned that there are nefarious intentions that could lead to an actual security or public safety incident?” There is nothing known that would lead me to make that statement, but we just don’t know. And that’s the worrying part of it.”

He told members of Congress that more than 3,000 sightings were reported last week to a tip line set up by the FBI, but so far there has been no breakthrough.

The admission that the country’s top law enforcement agency is essentially ignorant of the mystery underscores the confusion that continues. It is not known whether a group or individual is behind the phenomenon, or whether there is even a credible problem – it has been speculated that the flurry of activity is simply confusion over sightings of regular aircraft, or the result of social media bias could .

Sightings have been reported in eight New Jersey counties. Mayors in 21 cities in the north and central parts of the state have written a joint letter to Murphy calling for statewide action.

Concern has focused on drones spotted near President-elect Donald Trump’s Bedminster golf course, as well as sensitive infrastructure such as electrical landmarks, train stations and police departments.

Recently, sightings have spread to parts of New York City and the Philadelphia suburbs. Nicole Malliotakis, a Republican congresswoman who represents Staten Island and parts of Brooklyn, told the House hearing that drones had been reported over the Verrazzano Narrows Bridge near U.S. military bases.

“They are flying over sensitive infrastructure, and the fact that we don’t know what they are, who is behind them or what they are doing is of great concern to me, especially in a post-China spy balloon world,” she said, according to a report in the local Morristown Daily Record.