The incident comes at a time of frayed ties between Washington and Beijing over issues including Taiwan, which China regards as its territory, and the shooting down of an alleged Chinese spy balloon that flew over the United States this year.

"The United States' long-term and frequent sending of ships and planes to conduct close surveillance on China seriously harms China's national sovereignty and security," foreign ministry spokeswoman Mao Ning said when asked about the latest incident.

"This kind of provocative, dangerous activity is the cause of the security issues on the seas," Mao said, calling on Washington to "immediately stop this form of dangerous provocation".

"China will continue to take all necessary steps to resolutely protect its own sovereignty and security," she said.

The US military said on Tuesday a Chinese fighter pilot had performed an "unnecessarily aggressive maneuver" near an American surveillance aircraft operating over the South China Sea last week.

Video footage released by the US military shows a Chinese fighter plane crossing in front of the American aircraft, which can be seen shaking from the resulting turbulence.

The Chinese plane "flew directly in front of and within 400 feet of the nose of the RC-135, forcing the US aircraft to fly through its wake turbulence" on Friday, the Indo-Pacific Command said in a statement.

"The RC-135 was conducting safe and routine operations over the South China Sea in international airspace, in accordance with international law," it said.

But China's military said on Wednesday the US jet "broke into" a military training area.

"A US RC-135 reconnaissance plane deliberately broke into our training area to carry out reconnaissance and interference," Chinese military spokesperson Zhang Nandong said in a statement.

China had sent aircraft to track and monitor the jet "in accordance with laws and regulations", Zhang said.

- 'Undermining mutual trust' -

The Pentagon said the incident was part of a pattern of behaviour by China.

A senior US defence official said there has been an "alarming increase in the number of risky aerial intercepts and confrontations at sea" by Chinese aircraft and ships -- actions that "have the potential to create an unsafe incident or miscalculation".

The announcement of the latest incident came a day after the Pentagon said Beijing had refused a US invitation for Defense Secretary Lloyd Austin to meet his Chinese counterpart in Singapore this week.

The senior US defence official said the timing of the announcement of the South China Sea incident was unrelated to China's refusal of the invitation, explaining that information "was subject to the US military declassification process and US diplomatic communication process".

Beijing said in response to reports of the Singapore cancellation that the United States was "entirely responsible for the current difficulties in exchanges between the two militaries".

"On the one hand, the United States keeps saying that it wants to strengthen communication," Chinese defence ministry spokesman Tan Kefei said Wednesday.

"But on the other hand, it ignores China's concerns and artificially creates obstacles, seriously undermining mutual trust between the two militaries," he said.

Austin and other US officials have been working to shore up alliances and partnerships in Asia as part of efforts to counter what they say are increasingly assertive moves by Beijing.

But there have also been tentative signs that the two sides were working to lower the temperature.

US National Security Advisor Jake Sullivan and top Chinese diplomat Wang Yi met in Vienna this month, and President Joe Biden said later that ties between Washington and Beijing should thaw "very soon".