The Pentagon has released a selfie taken in the cockpit of a U-2 spy plane, as an Air Force pilot flew above the large suspected Chinese surveillance balloon before it was shot down by the US military this month.

The selfie image, taken by the pilot of the U-2 on February 3, shows the shadow of the aircraft on the balloon and a clear image of the balloon's payload as it crossed across the continental United States.

The balloon, carrying a payload the size of three coach buses, was first spotted by the US military on January 28 and ultimately shot down by a US Air Force fighter jet off the coast of South Carolina on February 4 after crossing the country.

The US defence department did not identify the U-2 pilot in the selfie but the authenticity of the image was confirmed during a Pentagon briefing on Wednesday by Deputy Pentagon Press Secretary Sabrina Singh.

Addressing a media briefing, Singh said that the search operations to recover sensors and other debris from the balloon which tumbled into the Atlantic Ocean concluded last week.

She said that "the majority of the balloon, including the payload, was recovered." A senior State Department official said earlier this month that fly-bys "revealed that the high-altitude balloon was capable of conducting signals intelligence collection operations." US officials said they decided against shooting the balloon down over the country because of its size, fearing falling debris could hurt civilians or property on the ground. Gen. Glen VanHerck, commander of US Northern Command and North American Aerospace Defense Command (NORAD), later said the balloon was 200 feet tall with a payload that weighed a couple of thousand pounds.

The US sent up U-2 spy planes to track the balloon's progress, according to officials.

The Chinese balloon was said to be hovering at 60,000 feet in the air. U-2 spy planes routinely fly at altitudes over 70,000 feet, according to the US Air Force.

The U-2 single-seater reconnaissance and surveillance aircraft were previously flown by the CIA.

US National Security Council spokesperson John Kirby said at a recent news briefing that the recovered material was now at the FBI laboratory in Quantico.

"It's quite a bit - it's a significant amount - including the payload structure, as well as some of the electronics and the optics," he said.

China has maintained that the balloon was a weather ship blown off course and criticised the use of force to bring it down as an "overreaction" and a violation of international norms.

But the US says the balloon was part of a sprawling Chinese intelligence collection programme on America and its allies.

The downing of the Chinese balloon has escalated the diplomatic and military strain between the world's two largest economies.

What was meant to be a high-profile visit for Secretary of State Antony Blinken to China earlier this month instead transformed into a standoff, testing President Joe Biden's resolve at a new moment of reckoning with Beijing, which has increasingly flexed its muscles in the Indo-Pacific and elsewhere.

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