There is no threat to national security or public safety from reported sightings of mystery drones that have stirred concern in parts of the United States, government agencies said Tuesday.

Residents of the country's northeast have for weeks been reporting flights of unidentified drones, a phenomenon that has sparked worries over possible foreign involvement as well as accusations of a US government cover-up.

"We have not identified anything anomalous and do not assess the activity to date to present a national security or public safety risk over the civilian airspace in New Jersey or other states in the northeast," the Department of Homeland Security, the Department of Defense, the FBI and the Federal Aviation Administration said in a joint statement.

"Having closely examined the technical data and tips from concerned citizens, we assess that the sightings to date include a combination of lawful commercial drones, hobbyist drones, and law enforcement drones, as well as manned fixed-wing aircraft, helicopters, and stars mistakenly reported as drones," they said.

Top US officials have previously rejected any suggestion of foreign involvement -- including far-fetched claims that the drones originated from an Iranian or Chinese "mothership" out at sea -- even as public concern has mounted.

But video footage of recent mysterious airborne phenomena has continued to clog social media, with sightings reported in states including New York, New Jersey, Maryland and Virginia.

President-elect Donald Trump has said the US government "knows what is happening," suggesting there is some sort of cover-up, but outgoing President Joe Biden's administration has rejected such suggestions.

© Agence France-Presse