The row between China and the United States over surveillance balloons deepened on Monday, with Beijing accusing Washington of more than ten incursions since the beginning of last year.

Chinese Foreign Ministry spokesperson Wang Wenbin said US high-altitude balloons had flown over its airspace "more than ten times without any approval from Chinese authorities."

Wang did not provide further details, but urged the US to "change its course and introspect itself rather than smear and accuse China."

Meanwhile, White House national security spokesman John Kirby told broadcaster MSNBC that China's accusation were "just absolutely not true."

"We are not flying balloons over China," Kirby added.

China's claims came after the US shot down what it says was a Chinese "spy balloon" off the coast of South Carolina earlier this month.

The US military has subsequently shot down three other flying objects over North America.

US on a hunt for flying objects

It was not clear where the three aerial objects downed over North America in the past three days came from.

"We're calling them objects, not balloons, for a reason," General Glen VanHerck, the commander of the US Northern Command and North American Aerospace Defense Command (NORAD), said on Sunday.

He added, however, that part of the reason for the repeated shootdowns was a "heightened alert'' following the incursion of the balloon from China.

VanHerck said the US adjusted its radar so it could track slower objects.

"With some adjustments, we've been able to get a better categorization of radar tracks now," he said, "And that's why I think you're seeing these, plus there's a heightened alert to look for this information."

Pentagon officials said they were still trying to determine what exactly the objects were.

The downing of the object over North American airspace has no peacetime precedent.

"I believe this is the first time within United States or American airspace that NORAD or United States Northern Command has taken kinetic action against an airborne object," VanHerck said.

UK to review airspace security

Defence Secretary Ben Wallace said that the United Kingdom would review its security plans in the wake of the suspected Chinese surveillance balloon into the US.

"The UK and her allies will review what these airspace intrusions mean for our security. This development is another sign of how the global threat picture is changing for the worse," Wallace told the Telegraph newspaper late on Sunday.

The paper reported that the security review would be used to help decide whether changes need to be made to the surveillance of British airspace.

lo/fb (AFP, AP, Reuters)