None of the mysterious drones reported over the skies of the U.S. Northeast are being flown by the Pentagon or are part of secret government tests, a Defense Department spokesman said Tuesday.

Major General Pat Ryder told reporters that top department officials take seriously any cases of drones flying near or over U.S. military sites, though he added this was not a new concern given the volume of daily drone flights.

"We will typically, when we detect them, attempt to classify them and take appropriate measures,” Ryder said. "Is it possible that some of those are surveilling? Absolutely. But can you make that assumption in every case, not necessarily.”

President Joe Biden on Tuesday night said, "We are following this closely. So far, no sense of danger.”

On Monday, White House national security spokesman John Kirby told reporters that "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 even stars that were mistakenly reported as drones.”

He added that the sightings were not deemed to be a national security or public safety risk.

Earlier that day, President-elect Donald Trump said, without citing evidence, that the U.S. military knew where drones took off from.

More than 1 million drones are registered to fly in the U.S., with around 8,500 in flight on any given day, a vast majority of which are recreational or hobbyist used for architectural, engineering, farming or law enforcement purposes, Ryder said Tuesday.

"Is it possible that some of those drones could be up to malign activity? It’s entirely possible, but the vast majority, that is not the case,” he added.