China warns U.S.: Stop spy flights

• China tells U.S. to end surveillance flights off its coast


• U.S. says Chinese fighter jet made dangerous, unprofessional passes near U.S. patrol plane


• Chinese defense ministry disputes U.S. claims


• China: U.S. spies on Chinese military drills, weapons tests

Hong Kong (CNN) -- China has warned the United States to end its military surveillance flights near Chinese territory, rejecting claims by Washington that a Chinese fighter jet made several "dangerous" and "unprofessional" passes at a U.S. Navy plane last week.

The U.S. should take "concrete measures" towards ending reconnaissance operations off the coast of China if it wants to improve bilateral ties between the two countries, a spokesperson for China's Defense Ministry, Yang Yujun, said at a regular press briefing in Beijing on Thursday.

On August 19, a Chinese fighter jet intercepted a U.S. Navy Poseidon patrol plane in the South China Sea about 135 miles east of the Chinese island of Hainan, coming as close as 20 feet at one point, according to the Pentagon.

The armed Chinese aircraft crossed close beneath the P-8 Poseidon three times, according to U.S. Defense Department spokesman Rear. Adm. John Kirby, who described the maneuvers as "pretty aggressive, very unprofessional."

Lockheed engineers are developing a hypersonic aircraft that will go twice the speed of the SR-71 Blackbird, which goes three times the speed of sound. That aircraft, seen in this photo illustration, is called the SR-72 or "Son of Blackbird." Take a look through the gallery to see other stealth and spy planes.

An SR-71B Blackbird flies over snow-capped mountains in 1995.

An A-12 reconnaissance aircraft, the predecessor to the SR-71, is seen on display at the Intrepid Sea, Air and Space Museum in New York City in August 2010.

The EP-3E Aries II aircraft is a reconnaissance aircraft that uses electronic surveillance equipment for its primary mission. One of them was in the news in April 2001 when it collided with a Chinese jet.

The F-117 Nighthawk is one of the most famous and successful stealth aircraft. It was the first plane to be completely designed around the aspect of stealth, and its development was kept a secret in the early 1980s.

Lockheed's "Have Blue" prototype was the predecessor of the famed Nighthawk.

The Northrop YB-49 was not considered stealth aircraft, but its "strategic bomber" design set the foundation for the B-2 Spirit, a future stealth bomber.

A B-2 Spirit soars over the Pacific Ocean in May 2006.

The Lockheed YF-12 flies a test mission near Edwards Air Force Base in California.

The YF-22A fighter, first produced in 1990, used stealth technology and became the first fighter-type aircraft to achieve sustained supersonic flight without employing afterburner.

The F-22 Raptor interceptor, which uses stealth technology, completed its first successful flight in 1997.

The MQ-1 Predator is an unmanned aircraft, or drone, that has conducted reconnaissance and surveillance missions.

In the 1950s, aircraft like these RB-47s conducted surveillance missions over the Soviet Union and other "denied areas," but they became increasingly vulnerable to enemy defenses.

The Convair RB-36D was the jet-augumented version of the U.S. Air Force's intercontinental strategic bomber. The bomb bay was fitted with 14 cameras, and the No. 2 bay was used to carry 100-pound photo flash bombs for nighttime aerial photography.

The U-2 high flying spy plane, developed by Lockheed, was considered stealthy because of its ability to fly at extremely high altitudes. But the Soviet Union's defense radar was still able to detect the aircraft.

CIA pilots stand in pressure suits in front of a U-2 plane. The pilots needed the pressure suits for the extremely high altitudes.

Eyes in the sky, seen and unseen

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Stealth and spy planes

It was the fourth such incident this year, according to the Pentagon.

China pilot 'professional'

Yang dismissed the claims Thursday, saying that the pilot had been "professional" and that "due regard" had been given to safety.

He accused the U.S. of focusing on the distance between the aircraft during the encounter while ignoring the fact that its military had been conducting frequent surveillance missions against China, which he said was a policy issue.

"On the one hand, the U.S. expressed their willingness to deepen a military-to-military relationship with China, but on the other hand, they are reluctant to give up these frequent close-in reconnaissance activities against China," Yang said.

U.S. military ships and aircraft have long been conducting "wide-ranging" surveillance activities near China, undermining Beijing's security interests and damaging bilateral ties between the two countries, Yang said, warning that the missions could lead to "undesirable incidents."

Yang accused the United States of spying on Chinese military exercises, trainings and weapons tests in the air and at sea.

"These behaviors of U.S. military ships and aircraft could easily cause misperception and miscalculation or even air and sea accidents. Therefore we do urge the U.S. side to decrease these close-in reconnaissance activities against China towards a complete stop."

He said China had expressed its concerns to the United States through multiple channels, including diplomacy.

Asked how China would respond if the United States failed to end its surveillance operations, Yang said the Chinese military's future missions would be decided based on "various factors," without elaborating further.

Yang dismissed claims by State Department spokesperson Jen Psaki Monday that U.S. surveillance activities are conducted in a transparent manner and that other countries, including China are made aware of Washington's plans.

"There has not been any notification to the Chinese side," he said.

Past encounters

In April 2001, a Chinese fighter jet and a U.S. patrol plane carrying a crew of 24 collided off Hainan, forcing the U.S. craft to make an emergency landing on the island.

Blaming the United States for the incident, Chinese officials said their J-8 fighter crashed into the South China Sea -- killing the pilot.

The United States called for the immediate return of the high-tech EP-3 aircraft and the crew.

The crew were allowed to return to the United States 11 days after the collision, and the dismantled spy plane was flown home some weeks later.

The United States conducts around 500 reconnaissance missions near China each year, according to Chinese military analyst Zhang Junshe.

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CNN's Tom Cohen contributed to this report.