Beijing blamed U.S. "provocation" Wednesday for an incident last week in which a Chinese plane crossed in front of an American surveillance aircraft over the South China Sea.
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 U.S. 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 U.S. 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 U.S. 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 U.S. jet "broke into" a military training area.
"A U.S. 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.
The Pentagon said the incident was part of a pattern of behaviour by China.
