White House unable to verify some drone sightings amid 'urgent concern' over mystery activity

Members of Congress continue to demand answers on mysterious drone activity on the East Coast that has alarmed residents and officials, with several senators expressing "urgent concern," as the White House downplayed concerns over some of the sightings.

The New York and New Jersey senators have asked the heads of the FBI, Federal Aviation Administration and the Department of Homeland Security to brief them on the issue in a new letter.

"We write with urgent concern regarding the unmanned aerial system (UAS) activity that has affected communities across New York and New Jersey in recent days," a letter dated Wednesday from New York Sens. Chuck Schumer and Kirsten Gillibrand and New Jersey Sens. Cory Booker and Andy Kim stated.

They asked to be briefed "as soon as possible on how your agencies are working with federal and local law enforcement to identify and address the source of these incursions."

The letter said there are potential safety and security risks posed by the large drones, which have been observed near "critical infrastructure and sensitive locations, including reservoirs and military installations."

Local and state officials have been calling for greater action and transparency on the unexplained drone sightings reported in the Northeast, particularly in New Jersey, where one state senator has called for a limited state of emergency in response to the activity and nearly two dozen elected officials from one impacted county have demanded a full investigation.

There have been reports ranging from four to 180 sightings per night, according to New Jersey Assemblywoman Dawn Fantasia, who attended a closed-door meeting on Wednesday with other state leaders and representatives from the Department of Homeland Security regarding the New Jersey drone activity.

The drones "operate in a coordinated manner" and have not been identified as hobbyist drones or ones related to DHS, she said.

It remains unclear who is operating the drones, according to a DHS handout released by Montvale Mayor Mike Ghassali, who attended the meeting.

"At this time, according to the FBI, there are no known specific or credible threats related to these sightings," the handout stated.

White House national security spokesman John Kirby told reporters Thursday that they have been unable to "corroborate some of the reported sightings" using their detection techniques, but are still investigating.

"Many" of the reported drone sightings appear to be lawfully operated manned aircraft, he said.

"We have no evidence at this time that the reported drone sightings pose a national security or a public safety threat, or have a foreign nexus," Kirby said. "The Department of Homeland Security and the FBI are investigating these sightings, and they're working closely with state and local law enforcement to provide resources using numerous detection methods to better understand their origin."

There have been no reported or confirmed drone sightings in any restricted airspace, he noted.

"That said, we certainly take seriously the threat that can be posed by unmanned aircraft systems, which is why law enforcement and other agencies continue to support New Jersey and investigate the reports, even though they have uncovered no malicious activity or intent at this particular stage," Kirby said.

Mine Hill Mayor Sam Morris, one of the elected officials in Morris County who demanded action over the drones in a letter sent to New Jersey Gov. Phil Murphy earlier this week, called Kirby's remarks "ridiculous."

"So what that means, he's saying we're all seeing small planes, that's my take on that. I have to tell you ... I'm incredulous about that," Morris told ABC News Live on Thursday. "I would invite Mr. Kirby to Mine Hill -- come on out, Mr. Kirby -- and let's go on out one night, about 9:30, 10 o'clock. I'll go out behind my town hall and you can count them with me all night."

He said one resident told him there's "anywhere from 30 to 40 a night" in the same area over the town of Roxbury.

"I have to say to Mr. Kirby, that's a lot of nonsense," he added.

Murphy said on his call-in radio show that he will be in touch with the White House on Thursday about the drone activity. ABC News has reached out to his office for an update.

House Speaker Mike Johnson said he will be receiving a classified briefing Thursday on the mysterious drone activity, calling it a "quandary."

"I'm anxious to find out," Johnson said about the drones.

The speaker declined to provide further details on the briefing.

The Pentagon said there is no evidence the drone activity is coming from any foreign entity or is the work of an adversary, refuting New Jersey Rep. Jeff Van Drew's claim that they could be coming from an Iranian mothership off the East Coast.

"There is not any truth to that -- there is no Iranian ship off the coast of the United States, and there's no so-called mothership launching drones towards the United States," deputy Pentagon press secretary Sabrina Singh told reporters Wednesday.

"We're going to continue to monitor what is happening," she said, adding, "At no point were our installations threatened when this activity was occurring."

A spokesperson for the FBI, which is the lead agency investigating the sightings, said it is "doing all we can [to] figure out what's going on."

"The public can continue to call our 800 line, or submit a tip online, we are acting on every substantive lead that we get," the FBI spokesperson said.

The FAA has imposed flight restrictions over Picatinny Arsenal in Morris County and Trump National Golf Club Bedminster in Somerset County in response to the drone activity.

The U.S. Northern Command (NORTHCOM) is also monitoring reports of "unauthorized drone flights in the vicinity of military installations in New Jersey," a spokesperson said.

"Local law enforcement and the FBI are currently investigating," the spokesperson said in a statement on Wednesday, adding that at this time NORTHCOM has not been requested to assist with the events but is prepared to respond "when asked or should the situation escalate to threaten any DoD installations."

ABC News' Alexandra Faul and Lauren Peller contributed to this report.