The US believes a suspected Chinese surveillance balloon that was shot down over its territory is part of a wider fleet that has spanned five continents.

“The United States was not the only target of this broader programme,” Secretary of State Antony Blinken said.

He added that the US had shared information gathered from the balloon debris with dozens of other countries.

China has denied the balloon was being used for spying purposes, and says it was a weather device blown astray.

US officials have described the balloon as being about 200 ft (60m) tall, with the payload portion comparable in size to regional airliners and weighing hundreds - or potentially thousands - of pounds.

It was shot down by a fighter jet over the South Carolina coast on Saturday, a move that set off a diplomatic crisis and prompted Secretary Blinken to immediately call off a trip to China - the first such high level US-China meeting there in years.

Citing unnamed officials, the Washington Post reported that the US believes the suspected surveillance balloon project was being operated from China's coastal Hainan province and targeted countries including Japan, India, Vietnam, Taiwan and the Philippines.

At a Wednesday news conference, Defence Department spokesman Brigadier General Pat Ryder confirmed that the US believed similar balloons had operated over North and South America, South East Asia, East Asia and Europe.

“We've learned a lot about these balloons and how to track them,” Gen Ryder said, adding that the US was now confident it had the ability to be “on the look-out for these kinds of capabilities”.

He said while the objects were all used for surveillance missions, there were “variations” in terms of their size and capabilities.

The US believes that balloons have operated over US territory on at least four occasions, but Gen Ryder did not give further detail on these instances.

Washington briefed 40 allied countries about the alleged espionage programme earlier this week, a senior Biden administration official confirmed to CBS News, the BBC's US partner.

Naval and Coast Guard ships and divers are still searching for debris from the balloon. It is unclear what intelligence the US has so far gleaned from the remnants, although experts say that the debris could help officials better understand what the balloon was capable of and how it transmitted information. (BBC)

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