Joe Biden has weighed in on public anxieties surrounding the large number of drone or other aerial objects moving in the skies above New Jersey and the US north-east, saying there is nothing alarming about the increased reports.

“Nothing nefarious apparently, but they’re checking it all out,” the president told reporters. “We’re following this closely, but so far, no sense of danger.”

Biden’s remarks come as John Kirby, the White House national security communications adviser, said the drones were not a national security or public safety risk. The Biden administration has been eager to remind nervous citizens in the tri-state area of New Jersey, New York and Connecticut that there were more than 1m drones registered with the federal aviation administration (FAA).

“There’s a lot of drones authorized up there,” the president said. “I think one started it and they all – everybody wanted to get in the deal.”

To allay public fears, the federal government is sending three mobile radar systems to the area that are better equipped to track a large number of objects. Officials have said night sky watchers may be looking at commercial planes and star formations, in addition to drones.

Biden’s remarks came after a small-town New Jersey mayor advanced a circulating theory that the drones could be looking for radioactive material that went missing from a damaged shipping container at the Port of Newark. According to a Nuclear Regulatory Commission alert, radioactive material went missing on 2 December.

“We know we have drones flying in a grid-like pattern,” said Michael Melham, the mayor of Belleville. “In my opinion, they’re looking for something. What might they be looking for? Maybe that’s radioactive material.”

Melham added: “Information has not been forthcoming, and it’s this lack of transparency … that’s doing nothing but fueling conspiracy theories online”.

But the mayor also sought calm nerves. “We know for a fact it’s not little green men … and more than likely, it’s not a foreign adversary, because they would be able to figure out how to turn off the blinking lights.”

Still, the political consequences of the drone debate are starting to proliferate, with area Democrats both defending and expressing exasperation at the administration’s assurances of no threat to public safety while providing what they believe are insufficient explanations for what people are seeing.

“It’s all about information and briefings, which has been my complete frustration,” said Josh Gottheimer, a Democratic congressman. “I’ve asked the FBI and DHS [department of homeland security] to actually do a proper public briefing.”

Earlier this month, Jeff Van Drew, a Republican New Jersey congressman, said baselessly that satellite confirmation of the departure of a militarized drone ship from its port in Iran could indicate that the night-flying drones could be from an Iranian drone mothership. He gave no evidence to support the theory.

At a press conference on Monday, Donald Trump also asked why officials had not been more forthcoming.

“The government knows what is happening. Look, our military knows where they took off from – if it’s a garage, they can go right into that garage,” Trump told reporters.