China has been operating a high-altitude balloon program spying on the US and its allies for many years, the White House said on Monday as it answered questions about a series of mysterious objects shot down by the US military over an eight-day period in North American airspace.

The surveillance program, according to John Kirby, the US national security council spokesperson, dated back to at least the administration of Donald Trump, which he said was oblivious to it.

“It was operating during the previous administration, but they did not detect it,” Kirby said.

“We detected it, we tracked it. And we have been carefully studying to learn as much as we can. We know that these PRC [People’s Republic of China] surveillance balloons have crossed over dozens of countries on multiple continents around the world, including some of our closest allies and partners.”

The briefing took place amid growing criticism of the Biden administration for not revealing everything it knew about the unprecedented and extraordinary sequence of events beginning with the downing of a suspected Chinese spy balloon off the South Carolina coast on 4 February.

Biden, Kirby said, directed a broad assessment of China’s intelligence capabilities when he took office. In response to recent events, Kirby said Biden had also now directed an interagency team “to study the broader policy implications for detection, analysis and disposition of unidentified aerial objects that pose either safety or security risks”.

Kirby was unable to offer new details about the three most recent objects, including the missile strike on Sunday on an unidentified “octagonal” flying object above Lake Huron, Michigan, and other high-altitude objects shot down over Yukon, Canada, on Saturday and Deadhorse, Alaska, the day before.

But he said that authorities would know more once debris had been recovered from remote locations and analyzed. He said all three were much smaller and at a lower altitude than the Chinese spy balloon, but their origin, composition and purpose remained unknown.

“We assessed whether they posed any kinetic threat to people on the ground. They did not. We assessed whether they were sending communication signals. We detected none. We looked to see whether they were maneuvering or had any propulsion capabilities. We saw no signs of that,” he said.

“[But] while we have no specific reason to suspect that they were conducting surveillance of any kind, we couldn’t rule that out.”

He said all three were shot down in “an abundance of caution to protect the security, our security, our interest and flight safety”.

The Nato secretary general, Jens Stoltenberg, suggested on Monday the objects were part of a “pattern” of surveillance of the US and its allies by China and Russia, and an American air force commander said the US military had spotted Chinese spy balloons in the Middle East in “the recent past”.

Canada’s prime minister Justin Trudeau echoed those comments, saying: “I think obviously there is some sort of pattern in there. The fact that we are seeing this in a significant degree over the past week is a cause for interest and close attention.

Trudeau said that Canadian authorities had deployed “significant resources” to attempt to recover the object shot down over Lake Huron.

The Florida Republican Marco Rubio, vice-chairperson of the US Senate intelligence committee, claimed that unidentified aircraft had operated “routinely” over restricted American airspace for years.

“This is why I pushed to take this seriously & created a permanent [unidentified aerial phenomenon] taskforce two years ago,” he said in a tweet.

In a press briefing on Sunday, a senior air force officer said he could not eliminate the possibility of extraterrestrial activity. “I’ll let the intel community and the counterintelligence community figure that out. I haven’t ruled out anything at this point,” Gen Glen VanHerck, head of North American airspace defense command (Norad), said.

But at the briefing on Monday the White House press secretary, Karine Jean-Pierre, said that the objects did not come from outside Earth. “There is no indication of aliens or terrestrial activity with these recent takedowns. I wanted to make sure that the American people knew that,” Jean-Pierre said.

Melissa Dalton, assistant secretary of defense, echoed VanHerck, saying: “We have been more closely scrutinizing our airspace at these altitudes, including enhancing our radar, which may at least partly explain the increase in objects that we’ve detected over the past week.”

Beside aliens, CBS’s veteran national security correspondent, David Martin, on Sunday said officials also apparently could not rule out whether at least some of the unidentified aerial objects which had been shot down were so-called sky trash.

“Sky trash includes balloons that are put up by governments, that are put up by corporations, that are put up by research institutes, and probably just by private individuals, and not for nefarious purposes, but just to collect scientific data,” Martin said on CBS’s Face the Nation.

“In the past, the US just hasn’t paid much attention to those balloons, but this Chinese balloon was a game-changer. And now, certainly, the Biden administration does not feel it can simply let these other objects pass through American airspace.”

The Connecticut congressman Jim Himes expressed frustration with the White House on Sunday in an interview on NBC’s Meet the Press.

“I have real concerns about why the administration is not being more forthcoming with everything that it knows,” said Himes, who like Biden is a Democrat.

“In an absence of information, people will fill that gap with anxiety and other stuff. So, I wish the administration was a little quicker to tell us everything that they do know.”

Stoltenberg told reporters on Monday in Brussels that he suspected the incidents were part of an ongoing strategy of spying by Nato’s rivals.

“What we saw over the US is part of a pattern where China and also Russia are increasing surveillance activities on Nato allies,” he said, urging member nations to maintain vigilance.

Lt Gen Alexus Grynkewich, commander of US air forces central, appeared to back up Stoltenberg’s assessment, telling reporters on Monday that Chinese spy balloons were spotted transiting the Middle East in the recent past, according to foreignpolicy.com.

Meanwhile, Biden’s secretary of state, Antony Blinken, is reportedly weighing a meeting with his counterpart in China’s government, Wang Yi, at a three-day security conference in Munich scheduled to begin 17 February, according to Bloomberg. Blinken had postponed what would be the first visit to Beijing by a senior US diplomat since 2018 in response to the Chinese balloon’s intrusion.