A review of the large mysterious drones reported flying over parts of New Jersey in recent weeks has shown many are actually manned aircraft being flown lawfully, a White House official said on Thursday.

John Kirby, the White House national security spokesman, said there were no reported sightings in any restricted airspace. He added that the US Coast Guard had not uncovered any foreign involvement from coastal vessels.

“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, echoing statements from the Pentagon and New Jersey’s governor, Phil Murphy.

Separately on Thursday, one US senator called for mysterious drones spotted flying over sensitive areas in New Jersey and other parts of the mid-Atlantic region to be “shot down, if necessary”, even as it remains unclear who owns them.

“We should be doing some very urgent intelligence analysis and take them out of the skies, especially if they’re flying over airports or military bases,” said Senator Richard Blumenthal, a Democrat of Connecticut, on Thursday as concerns about the drones spread across Capitol Hill.

The drones appear to avoid detection by traditional methods such as helicopter and radio, according to a state lawmaker briefed on Wednesday by the Department of Homeland Security.

In a post on the social media platform X, the assemblywoman Dawn Fantasia described the drones as up to 6ft (1.8 meters) in diameter and sometimes traveling with their lights switched off. The Morris county Republican was among several state and local lawmakers who met with state police and homeland security officials to discuss the spate of sightings that range from the New York City area through New Jersey and westward into parts of Pennsylvania, including over Philadelphia.

The devices did not appear to be being flown by hobbyists, Fantasia wrote.

Dozens of mysterious night-time flights started last month and have raised growing concern among residents and officials. Part of the worry stems from the flying objects initially being spotted near the Picatinny Arsenal, a US military research and manufacturing facility; and over Donald Trump’s golf course in Bedminster. Drones are legal in New Jersey for recreational and commercial use, but they are subject to local and Federal Aviation Administration (FAA) regulations and flight restrictions. Operators must be certified by the FAA.

Most, but not all, of the drones spotted in New Jersey were larger than those typically used by hobbyists.

The number of sightings has increased in recent days, though officials say many of the objects seen may have been planes rather than drones. It is also possible that a single drone has been reported more than once.

Murphy and law enforcement officials have stressed that the drones do not appear to threaten public safety. The FBI has been investigating and has asked residents to share any videos, photos or other information they may have.

Two Republican Jersey Shore-area congressmen, Chris Smith and Jeff Van Drew, have called on the military to shoot down the drones.

Smith said a coastguard commanding officer briefed him on an incident over the weekend in which a dozen drones followed a motorized coastguard lifeboat “in close pursuit” near Barnegat Light and Island Beach state park in Ocean county.

Lt Luke Pinneo with the US Coast Guard told the Associated Press on Wednesday “that multiple low-altitude aircraft were observed in vicinity of one of our vessels near Island Beach state park”.

The aircraft were not perceived as an immediate threat and did not disrupt operations, Pinneo said. The coastguard is assisting the FBI and state agencies in investigating.

In a letter to the defense secretary, Lloyd Austin, Smith called for military help dealing with the drones, noting that Joint Base McGuire-Dix-Lakehurst had the capability “to identify and take down unauthorized unmanned aerial systems”.

However, a Pentagon spokesperson, Sabrina Singh, told reporters on Wednesday that “our initial assessment here is that these are not drones or activities coming from a foreign entity or adversary”.

On Tuesday, the senators of New York and New Jersey issued a letter to the homeland security department, the Federal Aviation Administration and the FBI, demanding a briefing on the drone sightings as soon as possible.

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In the joint letter, Senators Kirsten Gillibrand, Chuck Schumer, Cory Booker and Andy Kim urged the government agencies to “brief us 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”.

“In addition to potential privacy concerns raised by these aerial systems, we are also especially concerned about how these drones may harm public safety,” they said.

Meanwhile Illinois’s Democratic representative, Raja Krishnamoorthi, said to NewsNation on Wednesday that he thought China might be conducting the drones in the US.

“It’s a non-trivial chance … It’s definitely a possibility, and the likelihood that they can then access data that is collected by these drones is very high,” he said.

“You can easily imagine a situation where these drones are flying over sensitive sites in the DC airspace,” he added, referring to Chinese-made drones.

Many municipal lawmakers have called for more restrictions on who is entitled to fly the unmanned devices. At least one state lawmaker proposed a temporary ban on drone flights in the state.

“This is something we’re taking deadly seriously. I don’t blame people for being frustrated,” Murphy said earlier this week. A spokesperson for the Democratic governor said he did not attend Wednesday’s meeting.

The Republican assemblyman Erik Peterson, whose district includes parts of the state where the drones have been reported, said he also attended Wednesday’s meeting at a state police facility in West Trenton. The session lasted for about 90 minutes.

Peterson said DHS officials were generous with their time, but appeared dismissive of some concerns, saying not all the sightings reported had been confirmed to involve drones.

So who or what is behind the flying objects? Where are they coming from? What are they doing? “My understanding is [officials] have no clue,” Peterson said.