"The US should first reflect upon itself and change course, instead of smearing other countries and inciting confrontation," Foreign Ministry spokesperson Wang Wenbin told the media in Beijing.

The US government pushed back, however, rejecting accusations that it had flown several high-altitude balloons over China.

"Not true. Not doing it. Absolutely not true," said US National Security Council communications director John Kirby. "We are not flying balloons over China."

Earlier, Wang had gone on to say that it was "quite common for US high altitude balloons to enter into other countries."

Washington also sent "aircraft and warships" to gather information on China, the spokesperson noted, adding that this year 64 sorties had been recorded in the South China Sea.

China claims a large part of the disputed sea area. The international arbitration court in The Hague rejected the claims in 2016. Despite the ruling, Beijing is building military installations there.

"It's quite clear to the global community which country is the number one spy empire in the world," Wang said, referring also to US surveillance activities and its large spy network.

The US had monitored calls and chat messages by the leaders of European countries including Germany, France, Norway, Sweden and the Netherlands, the spokesperson said.

He reiterated that the Chinese balloon that entered US airspace last week was "an entirely unexpected isolated event caused by force majeure" and said he did "not have any information" on any of the other unidentified unmanned objects detected over the country.

Washington has now shot down an overall four unmanned objects, officials said on Sunday, with the latest being downed over Lake Huron on the order of US President Joe Biden.

"We were able to determine that China has a high-altitude balloon program for intelligence collection that's connected to the People's Liberation Army," Kirby told reporters at the White House on Monday.

"It was operating during the previous administration, but they did not detect it. We detected it. We tracked it. And, we have been carefully studying it to learn as much as we can," he said.

"We know that these [Chinese] surveillance balloons have crossed over dozens of countries on multiple continents around the world, including some of our closest allies and partners," Kirby said, adding that Washington was consulting with allies and partners on the subject.

Kirby also said that Biden on Monday directed an interagency team to study the broader policy implications for detection, analysis and disposition of these aerial objects, which he said pose either safety or security risks.