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."

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.