The FBI and DHS in a joint statement said "it appears that many of the reported sightings are actually manned aircraft, operating lawfully. There are no reported or confirmed drone sightings in any restricted air space."
White House spokesperson John Kirby told a news briefing that federal authorities were investigating the sightings in cooperation with New Jersey state and local law enforcement. Most of the sightings have been of aircraft operating lawfully, he said.
"While there is no known malicious activity occurring, the reported sightings there do, however, highlight a gap in authority," Kirby said.
He repeated White House calls on Congress to pass legislation to expand the ability of authorities to identify and counter drones that are a threat to airports or other critical infrastructure.
The Federal Aviation Administration said it began receiving reports of drone activity near Morris County, New Jersey, on November 18.
The Pentagon has said an initial assessment had shown the drones were not from another country. It said the US military had not shot them down because they did not pose a threat to military installations.
Asked if President Joe Biden's administration was considering prohibiting drone use in US airspace, Kirby said: "I don't know that we're at a stage right now where we're considering that sort of a policy option".
Tony Perry, mayor of Middletown, New Jersey, told CNN on Thursday that in the past week or so there have been more than 40 drones spotted over his town.
He said the drones are "SUV-sized" and fly at upward of 110km/h.
"I'm not sure how anyone can just sit there and say that there's no imminent threat," Perry said.
"I don't think the federal government has taken it seriously to date."
Perry said he and other local officials were told at a briefing on Wednesday by the New Jersey State Police and the Department of Homeland Security (DHS) that the Coast Guard is patrolling the state's coastline looking for any type of vessel that could serve as a platform for the drones.
Kirby said on Thursday the Coast Guard has confirmed there is "no evidence of any foreign-based involvement from coastal vessels"
On Wednesday, US senators representing New Jersey and New York sent a letter to the heads of the FBI, DHS and the Federal Aviation Administration, demanding a briefing on how the agencies are working to identify and address the sightings.
The letter from senators Kirsten Gillibrand, Chuck Schumer, Cory Booker and Andy Kim expressed "urgent concern" about the reported sightings, and asked for a briefing "as soon as possible."
