Questions about three unidentified flying objects downed by US Air Force jets over North America in three days intensified Monday, while Beijing and Washington traded accusations over using high-tech balloons to spy on each other.

Puzzlement, fear and in some political quarters growing anger reigned as demands mounted for President Joe Biden's administration to explain not just the origin of the objects but their purpose, potential threat, and number.

It's not clear whether the three latest unidentified flying objects -- shot down Friday over Alaska, Saturday over Canada, Sunday over Michigan's Lake Huron -- have any connection to a much bigger white balloon that was shot down over the Atlantic on February 4.

The US military, which tracked that balloon as it crossed much of the country, says it was a sophisticated, high-altitude Chinese spying device -- one of a fleet of such craft allegedly floating around the globe. Recovery teams are scouring the seabed to pull up the debris for analysis.

China insists that the balloon, which was big enough to be visible to ordinary Americans from the ground, was merely blown off course while collecting weather data. Chinese authorities also admitted that a balloon spotted over Latin America was one of theirs -- in this case a civilian device for flight tests.

On Monday, Beijing sought to turn the tables by accusing Washington of deploying more than 10 balloons into Chinese airspace over the last year.

"It's not uncommon as well for the United States to illegally enter the airspace of other countries," foreign ministry spokesman Wang Wenbin said during a briefing. The alleged flights were made "without any approval from Chinese authorities."

At the White House, National Security Council spokeswoman Adrienne Watson quickly called China's allegations "false" and said that China's high-altitude spying program has violated airspace of "40 countries across five continents."

The State Department said China was "scrambling to do damage control" and that the communist government "has failed to offer any credible explanations for its intrusion into our airspace."

Over the weekend, Chinese state-affiliated media reported that an unidentified flying object had been spotted off the country's east coast and that the military was preparing to shoot it down.

Beijing on Monday declined to comment on that report, referring journalists to the defense ministry, which did not respond to requests for comment from AFP.

Questions and few answers

In Washington, the extraordinary events are fueling already intense suspicion about China across both the Democratic and Republican parties -- a trend likely to grow as the 2024 presidential election approaches.

The diplomatic fallout has already been substantial, with Secretary of State Antony Blinken abruptly canceling a rare visit to Beijing.

Republican lawmakers Monday piled pressure on the White House to give answers about the scope and nature of the threat.

"How many more unidentified objects in US airspace before the Biden Administration gives us some -- ANY -- answers?" tweeted Republican Representative Mark Green.

Officials have issued little information about the three latest objects, other than to say they were much smaller than the confirmed Chinese balloon destroyed February 4. That was about the size of three buses, while the new targets were more car-sized.

"We're going to do everything we can to recover them," White House spokesman John Kirby told MSNBC on Monday. "As soon as we do that, we'll learn more."

The unidentified flying object shot down Sunday over Michigan was described by officials as an octagonal structure with strings hanging off it. However there was no information about how it was guided or propelled.

Canada's defense minister, Anita Anand, told CNN the object shot down over Canada by a US plane appeared to be "cylindrical" but said no more information would be given until "we gather the debris."

Amid often wild speculation, the US Northern Command's General Glen VanHerck was asked if the government could be sure these were not extraterrestrial craft and he replied: "I haven't ruled out anything at this point."

Why such a sudden spate of sightings is another unanswered question.

Assistant Secretary of Defense for Homeland Defense and Hemispheric Affairs Melissa Dalton said Sunday that this may be because the Pentagon has been "enhancing" its radars -- meaning smaller objects are now visible.