The U.S. intelligence community has linked the Chinese spy balloon shot down on Saturday to a vast surveillance program run by the People's Liberation Army, and U.S. officials have begun to brief allies and partners who have been similarly targeted.

The surveillance balloon effort, which has operated for several years partly out of Hainan province off China's south coast, has collected information on military assets in countries and areas of emerging strategic interest to China including Japan, India, Vietnam, Taiwan and the Philippines, according to several U.S. officials, who, like others interviewed for this story, spoke on the condition of anonymity because of the matter's sensitivity.

Officials have said these surveillance airships, operated in part by the PLA air force, have been spotted over five continents.

"What the Chinese have done is taken an unbelievably old technology, and basically married it with modern communications and observation capabilities" to try to glean intelligence on other nations' militaries, said one official. "It's a massive effort."

On Monday, Deputy Secretary of State Wendy Sherman led a briefing on China's balloon espionage for some 150 people from about 40 embassies, said a senior administration official familiar with the matter. The department has also sent to every U.S. Embassy a "detailed information" on the espionage that can be shared with allies and partners.

Separately, U.S. officials have begun to share specifics with officials in countries such as Japan whose military facilities were targeted by Beijing.

"There has been great interest in this on the part of our allies and partners," said a senior administration official.

"Many of them recognize that they, too, may be vulnerable or susceptible to this or an object of interest to the PRC," the official said, referring to the People's Republic of China.

In Japan in 2020, an aerial orb drew speculation. "Some people thought this was a UFO," said a Japanese official. "In hindsight people are realizing that was a Chinese espionage balloon. But at that time it was purely novel — nobody had seen this. . . . So there's a lot of heightened attention at this time."

While most of China's long-range surveillance efforts are conducted by its expanding military satellite array, PLA planners have identified what they consider to be an opportunity to conduct surveillance from the upper atmosphere at altitudes above where commercial jets fly, using balloons that fly between 60,000 and 80,000 feet or higher, officials said.

Analysts still don't know the size of the balloon fleet, but there have been "dozens" of missions since 2018, said one U.S. official. They take advantage of technology provided by a private Chinese company that is part of the country's civil-military fusion effort — a program by which private companies develop technologies and capabilities used by the PLA.

In a news briefing Saturday, senior Pentagon officials alluded to the PLA program, noting that balloons had been operating elsewhere in the Western Hemisphere. "These balloons are all part of a PRC fleet of balloons developed to conduct surveillance operations, which also violated the sovereignty of other countries," said one senior defense official.

The official flatly rejected China's assertion that the airship moving over the United States was a weather balloon blown off course. "This is false," the official said. "This was a PRC surveillance balloon. This surveillance balloon purposefully traversed the United States and Canada. And we are confident it was seeking to monitor sensitive military sites."

Some commentators have made light of the Chinese effort, noting that balloons are not the most high-tech of platforms. But others caution against dismissing the balloons' potential.

"For those who have a sanguine view about the actual intelligence collection capabilities of this balloon, I think they're underestimating the creative ways the PLA might use it either for intelligence and surveillance purposes, or as a platform for weapons," said Rep. Michael Gallagher (R-Wis.), chairman of the Select Committee on China, who was commenting on public remarks made by Pentagon officials over the weekend.

In recent years, at least four balloons have been spotted over Hawaii, Florida, Texas and Guam — in addition to the one tracked last week. Three of the four instances took place during the Trump administration but were only recently identified as Chinese surveillance airships. Other balloons have been spotted in Latin America and allied countries in the Pacific, officials have said.

President Biden directed that all sensitive sites were protected from espionage, "which was straightforward because we could track the path of the balloon and ensure no sensitive activities or unencrypted communications would be conducted in its vicinity," said National Security Council strategic communications coordinator John Kirby. "At the same time, we turned the tables on China and collected against the balloon, so that we would learn more about China's capabilities and tradecraft."

Monitoring the recent balloon helped fill in gaps about the four others, officials said. The U.S. military sent up fighter jets and other aircraft over the past week to observe the airship. A Chinese spy balloon that crashed off the Hawaiian islands last June also yielded helpful information, including about the nature of the technology China is using, they said.

For instance, some of the balloons are outfitted with electrooptical sensors or digital cameras that, depending on their resolution, can capture highly precise images, officials said. They also are equipped with radio signal and satellite transmission capability, they said.

Hainan, one of the locations where officials said the balloons are based, is an island off the southern coast of China that has long been a PLA command and control location. Though known more for its naval facility, it features an airfield that was the home base for the Chinese J-8 interceptor fighter jet that collided with an American EP-3 spy plane in 2001.

In January, the U.S. military disclosed what it characterized as an unsafe maneuver in December by a Chinese fighter jet that U.S. military officials said flew too close to an American reconnaissance aircraft in international airspace near the island. The Chinese J-11 fighter pulled within 20 feet of the American plane's nose, "forcing the RC-135 to take evasive maneuvers to avoid a collision," U.S. Indo-Pacific Command said in a statement.

The spy balloon shot down Saturday first entered U.S. airspace over Alaska on Jan. 28. It crossed north of the Aleutian islands, back over mainland Alaska, over Canada and then over northern Idaho last week, but the Pentagon did not acknowledge its presence until NBC News reported last Thursday that the Pentagon was tracking the balloon over Montana.

The resulting political uproar — some Republicans slammed the Biden administration for not shooting down the balloon sooner — led Secretary of State Antony Blinken to postpone a trip to Beijing, an announcement made hours before his plane was set to take off.

U.S. intelligence analysts have retroactively identified as spy balloons objects that were previously deemed unidentified, according to U.S. officials. New technologies have enabled the detection of measurement and signature intelligence, or MASINT, which typically includes information about radar or electromagnetic signals, such as those that might be emitted by surveillance balloons.

In some instances, the military and intelligence communities have been able to say that they originated in particular countries, including China, the officials said.

The retroactive discovery of the Chinese balloons helps explain why senior defense officials serving in the Trump administration were not aware of the incursions during their time in office, officials said.

China has made significant use of balloons to monitor targets on the ground, officials said. The balloons often don't use the most cutting-edge technology — in most cases, the sensors aboard don't capture more information than China could obtain with a satellite.

But balloons offer some advantages. They can linger over a target for hours, whereas a satellite orbiting Earth may have only minutes to snap a picture of its target. "If you have a balloon that's moving extremely slowly you have persistence that you can't get from a satellite," said retired Air Force Lt. Gen. Charlie "Tuna" Moore, a former fighter pilot who helped run operations out of NORAD and retired in October as deputy of U.S. Cyber Command.

Analysts think the balloons, like drones, can be remotely piloted — at about 30 to 60 mph, said one official. And because balloons float along high-altitude winds, their paths are less predictable and thus more difficult to track. The balloons are also much cheaper to produce and launch than space-based satellites.

Some of the balloons have been launched from China on flight paths that took them around the entire globe, officials said.

Officials noted that China's Ministry of Foreign Affairs was apparently caught by surprise and was chagrined to see Blinken cancel his visit. The ministry initially issued a statement, saying China "regrets that the airship strayed into the United States by mistake." Since then, Beijing has been contacting its neighbors to keep lines of communications open amid the burgeoning crisis — a signal, said one official in the Pacific region, that Beijing was embarrassed by the balloon's flight across the United States and trying to quell the controversy.

In a statement over the weekend, a Ministry of Foreign Affairs spokesperson appealed for maintaining "a coolheaded and prudent" approach to the incident.

A U.S. official said that "there was no sense that" the balloon's incursion into continental U.S. airspace on the eve of Blinken's visit was a deliberate provocation. But, the person added, "We are confident that this was a purposeful global program."

"China's foreign policy is a constant search for leverage and in most circumstances there are ample opportunities," said the official. "In this one, there would appear to be very few. So when the Chinese appeal for calm and coolheadedness you can be sure they're nearly out of options."

The Washington Post's Cate Cadell and Alex Horton contributed to this report.

previous coverage

• China balloon saga spotlights Beijing’s global spying push
• Massachusetts Air National Guard’s 104th Fighter Wing assists in shooting down suspected Chinese spy balloon
• Pentagon reports past Chinese surveillance balloons near Florida, Texas

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• Balloon incident shows ‘deep distrust’ between US and China, could yield ‘treasure trove’ of intel, experts say